Spa and Hot Tub Covers

Every week I get a call from someone wanting to know if we can build a custom spa cover.  The answer is yes with a qualification.  Not every spa can be covered.  Before you let work begin on that custom spa idea you should consider how you plan to cover it.  After the spa is built it will often be too late.

Spa manufacturers are building all sorts of shapes and sizes these days that can be purchased and delivered to your home and covered easily.  But for high end custom built spas, that often cost six figures it is not so easy.  Unfortunately far to often it is after the spa is complete and the owner gets their first heating bill that they think about a cover.

These spas are often featured in spa magazines and truly look amazing.  Who would not want one?  They look like theme park attractions you can own.  They often feature natural looking rock walls and water falls, spill ways and infinite edges so that while you sit on the spa you can see the landscape beyond.  All very impressive and expensive.  Unfortunately heating and keeping debris out of such a work of art can also be an expensive proposition.

If you ask the designer of one of these spas how they intended it to be covered when the spa was not in use, the answer is they do not want it covered.  That may not seem so bad if the spa is in southern California or some tropical island.  However even these places need to keep rain water and blowing debris out of the spa.  In snow country it becomes even more important to cover the spa when not in use.

If you are considering having one of these spas built, make sure the designer is including a cover into the process and that it does offer insulation.  Just having a safety cover anchored over the spa is not going to keep heat in or debris out.  To insulate the water when the spa has different heights around the edge such as a spillway, the spa cover should actually rest on the water.  By coming in contact with the water the insulating cover will cut down evaporation and chemical consumption too.

In order for the cover to be easy to attach and remove you also need to consider access around the spa.  If you have one side of the spa hanging off in space it may be attractive but fastening any cover on that side would be precarious without some consideration of how to safely maneuver around outside of it.

Likewise a spa buried in a rock wall.  If a wall of any kind rises up vertically, although beautiful will always be problematic for fastening and keeping stuff out of the spa.  Planning on a cover before built is the only way I know of to deal well with this.

There are solutions available to cover almost any spa if the cover is built into the initial design.  It will most likely be a costly spa cover and pricey to replace however not as expensive as leaving the spa uncovered.  The reason for the cost is that each time it is built is basically a one off production.  This is why most concept cars go straight to a museum.  If anything breaks on it there are no replacements sitting on a shelf somewhere.

Is that heavy foam cover the reason why? In Search of the Perfect Replacement Spa Cover? If you have had your hot tub for a few years you’ve probably bought a few foam covers. You probably bought the first replacement cover from the same place you bought your spa.

You went in and told the salesman that your cover got heavy. More than likely he told you that now they have developed a better foam cover. One wrapped, glued, dipped, sealed in multiple layers of special stuff. But even that one got heavy eventually.

One friend of mine just thought he was getting weaker, until he went to the spa dealer and looked at a new cover. Preparing to use as much effort to lift the new cover as he did his own at home, he nearly threw the cover through the front window of the store. It was then that he realized his cover was getting heavy. Like him you have most likely figured out that rigid foam spa covers are flawed technology.

All rigid foam spa covers will always eventually become moisture saturated, heavy, and might even break or blow away. Regardless of what wrapping is around the foam it is doomed to get heavy.

Even if it were possible to keep the foam from saturating with water no rigid cover is ever going to be in contact with the water that it is supposed to keep warm. Every rigid foam spa cover is constantly losing heat between the bottom of the spa cover and the water surface. As the spa water produces steam that steam hits the bottom of the cooler rigid foam spa cover, condenses and falls back into the spa actually cooling the water.

But the real point is that with a foam cover that slowly gets heavy we slowly stop using our spas. Generally speaking the foam fails slowly so you don’t notice it. If you use your spa every day, an ounce different here and there does not get noticed. It just becomes a little more work. So you just put up with it. But after while you get home from work and the thought of wrestling that cover off the spa just becomes less important.

That is a shame considering how much you looked forward to it when you first got your spa. It is also a shame considering how much you spend to heat the water that you are less willing to get into. It is a shame considering how much you paid of your hard earned money to get that spa in the first place. Did you know that the more time you spend in your spa the less sleep your body requires? If you got your spa for therapeutic purposes how often do you think you can afford to go without that therapy before you start to suffer?

Are you willing to loose all that just for the sake of a few inches of foam? I see it every day. People with spas in their back yard, but instead of using their spa they pile stuff on it. It might be the picnic table they moved just to make it easier to mow. Maybe it is toys the kids left out or the barbecue. Seems like an expensive place to pile your stuff but people do.

I propose you get back to enjoying your spa. Instead of replacing your heavy spa cover with another one that is just going to end up the same way, shop online for a different type of cover. Find a different type of spa cover that does not use foam so it will not get heavy. If you do, you can enjoy your spa for years to come. You will thank me later.

If you need a new spa cover because your old foam cover was damaged by the elements, consider something different. The typical rigid foam filled hot tub cover covered with vinyl is doomed to end up heavy or broken no matter how well you treat it.No matter what you treat it with all vinyl is rated by hours outdoors. Really top quality marine grade vinyl is rated for 1500 hours outdoors. That equates to about one hundred days of sunshine. I know what you are thinking, why would anybody put vinyl on something that is meant to be used outside? But that is not even the most common failure of the typical rigid foam filled spa cover.

What generally happens before the vinyl falls apart is that the foam gets so heavy you can not lift your spa cover by yourself. No matter how it is wrapped and sealed inside the cover, the foam fills with water. What happens is the little air spaces in the foam that are supposed to help the foam insulate your spa get filled up moisture. Here is a tip why the whole foam cover is doomed, if you never put the cover on your spa, it would never get heavy. If you just took a brand new spa cover out and put it on your picnic table instead of your spa, the vinyl would fall apart before the cover got heavy.

Why? Because the hot spa water is way below the bottom of the rigid foam spa cover. Some of that warm spa water turns to steam and rises up. Steam molecules are smaller than water. The steam works its way into the little crevices and spaces in the foam where it condenses back into liquid. If you live in an area that gets snow, the snow will land on the saturated foam and freeze the water inside it.

How? because just as heat rises, cold sinks. When it comes in direct contact with the foam it freezes the moisture. The warm spa water is not in direct contact with the bottom of the spa cover so it is in a loosing battle trying to beat the cold. The steam rises from the water, hits the bottom of the now frozen spa cover, condenses and falls back into the water below working like a radiator to actually cool the water.

You may look out at the snow piled on your frozen spa cover and think you have great insulation. But you would be wrong. Snow sits perfectly on a frozen pond too. It does not mean the pond water is still warm. So why does anybody still sell rigid foam covers? Well two reasons really. First, it has been the standard of the industry for nearly thirty years. When the acrylic spa began to be sold in the states, it needed to be covered with something to keep the debris out and to assist in keeping the water warm. Foam boards covered with vinyl was cheap and since everybody was selling the same thing it was all they needed to offer. Remember definition of insanity is to do the same thing over and over expecting a different outcome.

The second reason is worse in my opinion. Spa dealers know that the cover they are sending you home with will need to be replaced again because it will end up the same as the one you are replacing now. They know that like clockwork every couple years you are going to need to get another cover if you intend on using your spa on a regular basis.

So what are your choices? Thanks to the internet you now have the world at your finger tips. Look on line for a different kind of spa cover. Find a spa cover that is not covered with vinyl that is rated by hours if your spa is outdoors. There are Spa Covers available factory direct that do not use rigid foam that is just going to end up to heavy to lift. If you plan on using your spa for the rest of your life like I do, you owe it to yourself to get a better kind of spa cover.

We get a lot of inquiries from spa owners that are replacing their cover due to hail damage. Traditional rigid foam covers get hammered by hail because they do not absorb impact very well. The foam inside the cover is rigid enough to form a bridge over the spa, however it does not allow for impacts.

Branches, falling debris and large hail will pound the foam with enough force to damage or break the cover. As people who live in areas of heavy hail storms know, anything rigid is going to take a pounding. If you have been replacing covers because of this type of damage you have to ask yourself if there is some better way of covering your spa.

Let’s look at a few options. First you could opt for an Aluminum cover. This would be stronger than a foam filled spa cover, but it could be a little unwieldy because a one piece cover that size would need significant storage space. Not to mention even the slightest wind would make it a very large destructive frisbee.

Another option would be to go with a roll cover. These are very strong and essentially work like a portion of deck that you roll over the spa. The down side is they tend to collect small debris and allow it to get into the spa. Though strong they also offer little in the way of insulation.

Then you could choose to go for a reinforced rigid foam cover. One of the latest developments in this area is to have the foam glued to a board for strength. This would of course handle all but the most devastating hail storm. Only two caveats on this type of spa cover, it still will fly in a wind storm and with the added mass it will do serious damage to anything it lands on and it will still eventually become saturated. Once it is saturated a cover like this will be a four person job to open the spa.

The solution to this would be something that is able to give or absorb impacts. In Hollywood when a stunt man falls from a great height, he wants to land on something that will absorb his impact like an air bag. The air bag principle would work as a spa cover to guard against impact damage. Just like the stunt man landing on a cushion of air the same would be true of debris, branches and even severe hail.

Now the stunt air bag is designed to open and release air when it catches the stunt person so please do not use your air filled hot tub cover this way. However if your house is on fire and you have to jump out of the window aiming for the large air bag would probably save your life. I should note here that jumping on any spa cover would not be covered by the warranty.

No matter how fierce the storm or the hail stone an air filled spa cover will give or catch it without damage. We have tested them by driving golf balls into them at close range, dropping bowling balls on them and just having them in use around the country in areas that get severe hail storms. Before you replace another rigid foam spa cover because it broke shop online for a spa cover that will not end up the same way.

Heavy Broken Spa Covers Waste Energy. I saw this advertised on line the other day. When I went to check out the guys website, guess what he’s selling? Rigid foam spa covers that will end up heavy or broken, usually within two years. To me this is like a coat salesman telling you wet wind breakers won’t keep you warm, here you need to buy this new dry wind breaker and go play outside in the rain.

Instead of selling you something that won’t get heavy or broken he keeps selling the same thing, hoping you won’t notice. If you have had to replace a spa cover because it got heavy, maybe the question you should ask before you buy the next one is, Why?

What causes the foam spa cover to get heavy is that it traps moisture inside. Rigid foam board is used in lots of insulation applications. It can be used around refrigeration storage areas like in a super market. Layers of foam board can insulate the cool storage area while the customer area can be kept comfortably warm. But in this type of installation the foam is not subjected to hot moist air. As long as the foam stays dry it has a predictable insulation value. But if the foam were to have moisture in it instead of the little air spaces it uses to insulate, it would have no insulation value at all.

If you wanted to produce the perfect environment for a rigid foam board to become saturated it would be to put it over a source of warm, humid, steam. You couldn’t get water into it faster even if you tied it to the bottom of your swimming pool. Why? Because water molecules are bigger than steam molecules. Steam can get into smaller spaces faster than water. And once the steam cools, it condenses back into water, displacing air in the foam as it does.

Long before you notice the spa cover getting heavy, moisture has begun to replace the air spaces in your cover. When it does, the little insulation value that cover might have had, goes down dramatically. From whatever it may have been when you first put it on your spa it has gone down to as much insulation as a wet piece of plywood by the time you actually notice it got heavy.

You might get fooled into thinking that it is still insulating well because snow won’t melt off it. Unfortunately, you would be wrong. Snow won’t melt off a frozen pond either but it doesn’t mean the ice is insulating the water. When snow falls on a saturated foam spa cover, it freezes the moisture in the cover because it is laying directly on the cover. The water of your spa is never in contact with the foam since the foam is resting way up on top of the acrylic of the spa, usually about a foot above the water surface. What’s happening is the warm spa water is evaporating into steam. That steam is rising, because that is what heat does, until it hits the bottom of the frozen spa cover. Then the steam cools and turns back into water. The water, now cooled, falls, because that’s what cold does, back into the warm spa water, cooling it off.

So if you wanted to invent a radiator to cool off your warm spa water this would be the perfect design. Put a block of frozen foam over the water. Load it up with snow so it will keep the spa cover frozen and stand back and watch the power meter spin. Instead of buying another rigid foam spa cover that will positively end up like the one you are replacing now, shop online for one that is designed better. Look for a spa cover that will insulate the water from the water surface, without rigid foam.

Did you buy a cover lifter for your spa and then find out that it doesn’t really help when the foam gets saturated? Your not alone. The truth is every rigid foam spa cover eventually ends up either broken or saturated and heavy.

Years ago there was a woman who because of a severe back injury needed to get into her spa. Her doctor had instructed her not to lift more than ten pounds and that she should get spa therapy every day. Looking at her own spa cover she realized she would have to think of a better way. Necessity being the mother of invention she set out to build something she could use herself.

What she came up with was a design that was both easy to use and durable. Initially she would have been happy with something that kept the leaves out of the spa that she could manage herself. Insulation was less important than ease of use. However testing of the new design showed the added bonus of better insulation than the typical rigid foam spa covers. The new design allowed for the cover to rest on the surface of the water so it drastically reduced heat loss from evaporation. With less evaporation the chemicals used to keep the water clear and clean stayed more consistent. With the cover laying right on the water insulation began at the water surface which is important since that is what you’re trying to keep warm.

Using the water to support the spa cover allowed the new design to be able to withstand more weight as in snow loads, without collapse as rigid hot tub covers do. Since it uses air to insulate rather than the foam found in typical spa covers, the improved spa cover could absorb impact better too. So in areas that get brutal hail storms, her spa cover would not be damaged while traditional spa covers were pummeled.

The new spa cover design created a natural dome shape while on the spa causing wind to blow over without creating lift. If you live in an area that gets strong winds you already know that rigid foam spa covers will fly. I have seen people try all kinds of things to keep their foam covers on from cement blocks to heavy webbing straps.

Armed with this knowledge she figured that she was not the only spa owner that was sick of heavy spa covers, so she patented the idea and began to market her new spa cover. Unfortunately, this was in the days before the internet. Getting the word out required actually getting out and meeting people. She traveled the country doing home shows and fairs. She travelled to spa dealers all over the country trying to convince them to sell her cover.

Most spa dealers were not interested. They make a lot of money selling a cover that needs to be replaced every couple years. Others did not want to dedicate any of their limited floor space to show just a cover, especially one that cost more to them than the cheap covers made overseas.

Fortunately, thanks to the world wide web, you can research for yourself and find out all about this innovative design from the comfort of your home. Available right from the factory you can order a cover custom made for your spa. If your tired of replacing your spa cover with the same old thing, look for the next generation in spa covers. The air filled cover that insulates better and lasts longer than any rigid foam spa cover. The cover designed by a woman so she could use her spa by herself.

Every week we get customers calling to order a new cover for a spa they just got for free. Spas and Hot Tubs are expensive. They run in the thousands of dollars. When you first get your new spa you use it everyday. You invite your friends over to enjoy your new toy. You go to work with a smile on your face because you know that no matter what hits you, by tonight you’ll be soaking it away.

Then why, if this is so great, would anyone end up giving it away? And as it is leaving say, “The spa works great it just needs a new cover.” I hear it all the time. To me this is equivalent to giving away your car because it needs a new set of tires. After Years of hearing these words I began to investigate the source of this change.

It happens slowly, but see if any of this sounds familiar. When you first get the spa you use it religiously. It becomes a part of your regular routine. Over time though it becomes a little bit more of a struggle. The reason is that cover that came with the spa begins to get heavy. It does it so slowly that you don’t even notice. As you begin to struggle with it you might think to yourself, “I must be tired.” Eventually you’ll wait a few days between using it and when you go to use it again you realize that what was a fairly easy operation now requires two people and real effort.

What do you do? Most people get in their car and go back to the place they bought their spa from. What does the spa dealer say? “Well, yes the cover that came with the spa is our low end model. They always get saturated. But we have this new high end model that has a special wrapper, a sealed moisture barrier. Buy this one and your trouble will be gone.” You may even head home with a spa cover lifter because it all makes sense. Trouble is that even the new special cover will get heavy too. Too heavy even for the lifter.

In most cases you have had your spa for a few years by now. The struggle to get into it has outweighed the value of the stress relieved. After a rate increase from the local power company you shut if off and drain it. You probably can’t remember the last time you were in it anyway. It becomes a place to stack stuff. Eventually the cover caves in and you decide its time to reclaim this part of the yard. You give it away or sell it cheap just to get it out of the yard. As it is leaving with its new owner you say these words, “It works great, it just needs a new cover!”

Now if you are the benefactor of such a statement, let me give you a heads up. You too will end up in the same situation unless you find a way to break the cycle of covers that get heavy. If you are the spa owner that is just about to give up think about this, the definition of insanity is to do the same thing over and over expecting to get different results. Don’t let a cover be the reason you give up something you paid hard earned money for and once enjoyed so much. Look for a different kind of spa cover. I once had a lady order a new cover from me and she was excited to show it off to her neighbor that had the same heavy cover challenge. But in before she could show her friend the new cover, the neighbor had punched holes in the bottom of her spa, filled it with dirt and made it a planter. A very expensive planter, all for the want of a better spa cover.

These days most spa dealers offer a rigid foam cover with a taper. The theory being that the sloped shape will help the foam shed rain and moisture so it won’t get saturated.
Does this work? Well, it does help the spa cover shed rain. However that is not what causes the foam to saturate. You can prove this to yourself by performing a simple test. Buy a new rigid foam spa cover with as big a taper as you can find. Bring it home and carefully weigh it. A hanging weight will probably be most accurate and simple to read. Record the weight and date it. Put it on your spa and then to be absolutely sure that no rain or outside moisture gets to your new hot tub cover, put a tarp over the whole spa, cover and all.

If you weigh the cover once a week and record it with the date, you will know exactly when the cover begins to saturate. You may not notice it at first but if you keep records on the weight, the scale won’t lie. If you are keeping all the rain water totally away from the spa, why is it getting heavy?

The fact is that moisture does not enter the foam from outside. What gets into the foam is the steam from underneath the spa cover. The steam particles are much smaller than rain. the steam can get through the smallest hole. Since the warm water of the spa is a constant source of evaporating water it will always work its way into the spaces in the foam. So in fact, the only way to avoid having any rigid foam spa cover saturate is to never put it on your spa or never put water in your spa.

Other than making the spa cover more difficult to use, is saturation bad? Yes, in a foam spa cover, it is not the foam itself that has insulation value but the air spaces in the foam. Once those tiny air spaces are filled with water, the spa cover has as much insulation value as a wet piece of plywood. When the foam spa cover begins to soak up the moisture, the little insulation it did offer goes down dramatically.

So what is the solution? First, you could buy two or three hot tub covers. Always have one or two drying out in your garage. Once the foam spa cover is not over the evaporating water, it will begin to dry out , become light again. You can rotate it back on to the hot tub. A light spa cover won’t rip your bar lifter off the sides of your spa and you should be able to keep using the spa easily. Since all vinyl is rated by hours outdoors, you will still need to be buying new covers to replace the ones that fall apart.

The other choice would be to find a spa cover that does not use rigid foam.

Think you need a spa cover lifter? Most spa cover lifters are simply a metal bar bent into a large U shape, that goes across the center of your spa. You fold your hot tub cover over the bar and then push it off your spa. These “Bar Lifters,” actually work great as long as your hot tub cover is not too heavy.

The spa cover lifter was an after thought, an after market solution to a product that was already in use. It works fine provided the Hot Tub cover has not begun to saturate. Most spa owners buy one because their spa cover is already heavy. If that’s you, the lifter won’t help. The bar lifter does nothing to help you get the cover open halfway. You still have to lift the first half of the cover up to fold it over the bar all on your own. If you can’t do that now, the lifter will do no good.

If you are strong enough to lift your heavy saturated spa cover over the bar it will either rip itself in two on the lifter or the bar lifter itself will be ripped from its own pivot points because it is not meant to handle the weight of a saturated cover. The center seam of the typical spa cover was never meant to handle its own weight once it gets saturated.

The bar lifter does make a nice place to hang the spa cover. Again this requires a light weight spa cover to work easily. That means, if the reason you bought the cover lifter was to avoid having to replace your heavy spa cover, this is not the answer. You will still need to replace your typical rigid foam filled hot tub cover every couple of years to make that lifter effective. Which in most cases is more frequently then you replace it now. If not, you will begin to use the hot tub less. The harder you have to struggle to get into it, the less priority it has.

If you already have a spa cover lifter, you probably know all this. Don’t despair. You just need to set aside enough money to replace that cover, like clockwork, every one to two years. When you buy the new cover, store the old one in a dry place somewhere. When the new one spa cover is one year old you can rotate the old one back onto the spa. It will have lost the weight of the saturation once you took it off the spa. You can get some extra life out of your covers this way but the fix is not permanent because all vinyl’s will eventually crack and fall apart. If you add a new one every three years and throw out the oldest one, you can keep two drying while one is in use.

Don’t bother buying the most expensive foam spa cover you can find because they all fall victim to the same thing eventually and the cheap covers will last just as long with rotation. The other option for those that already have a bar lifter would be to buy a different type of cover that could still be used with the mechanism. There are some options out there, I would recommend you shop on line. Look for something that won’t weigh more that a typical foam spa cover and that can work in a similar way to lay over the bar. Just keep in mind the goal is to use your spa, not your lifter. You may have to adjust how or where it pivots from to accommodate a different kind of cover, but if it makes getting in and out of your spa easy that is the real bottom line.

I have seen a posting on a competitors website regarding a comparison of outside temperature of a rigid foam spa cover verses the outside surface temperature of a SpaCap. The information given there is an opinion of how well the cover works based on pointing a heat sensing gun at both covers while in use. Although the person doing the test may have performed the test accurately and may have used a very sophisticated testing device, they did not actually address the function of a spa cover, keeping the water in the spa warm while using the least amount of energy doing so. Let me start with a brief description of the difference between the two methods of covering the hot tub. First the traditional foam spa cover. A rigid foam cover lays across the surface of the spa on top of the Acrylic, like a bridge over the spa water. In most cases this rigid piece of foam is several inches off the water it is supposed to be keeping warm. Ten to twelve inches of gap between the hot tub water surface and the bottom of the spa cover is not unusual.

The SpaCap hot tub cover by comparison lays right on the waters surface and uses closed air chambers to insulate the spa water, similar to how the layers of glass on your storm windows insulate your house. The big difference to note in these two styles is the gap between the spa water and the cover being used to insulate it. The dirty little secret behind rigid foam spa covers is they can Never effectively insulate the spa water. Instead it just covers the spa, reducing, but not eliminating the steam that would otherwise rise off the water’s surface into the atmosphere. A rigid foam cover twelve inches thick would still allow the warm spa water to evaporate into steam, rise up, cool, and condense on the bottom of the cover (if you own one you have seen the droplets on the bottom). The condensation then falls back into the spa cooling the water causing the spa to work harder to keep the water warm.

Another thing that happens in rigid foam covers is saturation. You may notice this, as it takes more muscle to lift your cover off your hot tub. Because of the spa environment the steam from the spa water eventually seeps into the foam and condenses in the little air spaces inside. This begins to happen almost as soon as you put it in service. Since those little air spaces in the foam represent insulation, the little value it might have is gone rapidly long before you notice the cover gaining weight. Once the ambient air temperature gets down to freezing the moisture trapped in the foam freezes so in fact you are now trying to insulate your spa with a block of ice. If you were to point a heat sensing device at that frozen block of ice would read the same temperature as the ambient air. Does that mean it is perfect insulation? Unfortunately, no.

Herein lies the problem in the heat gun test. Since no rigid foam cover is actually in contact with the water it is supposedly keeping warm and it is in fact in contact with the ambient air above the spa, it is only natural that it would be more relative to the outside temperature. By comparison the SpaCap laying right on the water surface insulates the water in two ways. First, it severely reduces the open water surface by coming in direct contact with it. The spa water consequently cannot evaporate as it does under the foam cover. A side benefit of the reduced evaporation is that the spa chemicals will also stay more consistent and you will be able to use less to get the same results which aside from saving frustration also saves you money. The second way the SpaCap insulates is by using closed air chambers stacked one on top of the other to create barriers of air between the outside ambient air and the water in the hot tub. Think of it like layering your clothes. If you have one layer of clothing on you stay slightly warmer than you would walking around naked. Two layers of clothing on you trap another layer of air around your body and stay warmer. More layers of air equal more insulation so you put on a coat over your shirt, over your underwear. The same is true in the animal kingdom. An animal that has to keep warm traps air around its body with feathers or fur. As long as that system is in good condition the animal stays warm. If the feathers or fur looses their ability to trap air, say it gets covered in oil, then the animal quickly looses heat and dies. Why? Because saturated fur, feathers or foam does not insulate. Trapped air insulates consistently. A twelve year old SpaCap still insulates as well as the first day it was put in service as long as it is still holding air. If you were to point a heat sensing device at the outside of a SpaCap while it is in use it would read some measure of heat, higher than the ambient air. Does that mean it is not insulating? No, it simply means that it is not perfect insulation. A better test would be to place the heat sensor in the water since after all, this is the focus of the insulation. Reading the temperature of the water and how fast it lost heat under a rigid foam cover verses how fast it lost heat while covered with a SpaCap would be a more useful test. This test we have done a number of times over the years. The SpaCap beats every foam cover ever made in this test. There is no other rigid foam filled cover that even comes close enough to call it competition. In fact a saturated foam filled cover tests the same as a piece of wet plywood.
The SpaCap is several times better at keeping spa water warm than its nearest competitor. If energy efficiency is what you want get yours with all the insulation options and your SpaCap will pay for itself with the energy you save.