Radiant barriers and Mylar insulation systems.

Radiant barriers and Mylar insulation systems.
7.7 Total Score


Recently some  companies Like Hydropool, and Canadian spa Company (Walmart, Home Depot) have begun using reflective foils either alone or with EPS (expanded Polystyrene) backing as primary insulation in hot tubs for cold weather climates. Claims of insulation values from R-10 to R-30 + are being used to describe these reflective insulation systems.

The truth is reflective foils alone have an R value of Right around R-1 ! (Glacier Bay Insulation Testing, 2003). While these systems can have as much as R-4 value as completed assemblies under optimum installation parameters the evidence suggests that as an insulator in a hot tub they are of limited value and certainly nowhere near the R-20+ that can be achieved with an expanding foam insulation system.

First of all these reflective systems effectiveness decreases dramatically in colder climates (Minnesota department of commerce Oak Ridge National Laboratory for the U.S. Department of Energy, 2015) While they have some value for preventing heat energy getting into a system they are much less effective at containing heat in a system. With the Canadian Mortgage Housing Corporation going as far as to say “It’s cost benefit was the poorest of all insulating materials tested.” (CMHC, 2004).

The second problem is that the installation requirements to even reach the R-4 range require optimum installation parameters that are just not attainable in a hot tub. One problem is that the reflective foils are orientated vertically which dramatically reduces R-value due to increased convection (Green Building Advisor, 2011), and the barrier can not be properly sealed to maximise the reflective heat retention which again is a critical part of maximising the R value (Reflectix Inc Installation manual N16 Revised 2011) .

The reality is this is an inexpensive insulation that even in the best circumstance is a poor solution especially as used in hot tubs. the average assembled R value of this system is roughly R-2 per layer and it is only going to affect radiant heat. Convection losses, where the foil is not sealed to the shell and conduction losses  where the foil touches pipework will dramatically effect the performance of this system.

This cheap method of insulation is clearly not suited to this purpose.

I am not a fan of the brand at all. Old style pressure filtration, old style floor suction rebranded as “Self-cleaning” and worst of all radiant barrier insulation…

There is not a good case for these inexpensive Radiant barriers being effective in this application.

All we have to do is look at the building industry back in the 80’s when these radiant barrier systems came on the market, almost every single northern US state ended up issuing warnings against it, you notice you never ever see this shit in the building industry where they have to meet code regulations?

These systems are good at reflecting heat away from something but they are crap at containing heat in a system because they have no thermal mass.

We know that the best we can hope for in an ideal final assembly is about R-4.7 per layer… But in a hot tub, we cant get anywhere near ideal assembly parameters and the reality is we are likely looking at about R-2 per layer. the actual Mylar film is only R-1 but again the final assembly which means the way it is installed can in ideal parameters (in an attic or on the bottom of duct work) can increase that to a maximum of around R-4.7 which is still way way less than the R-20 we can get with expanded foams.

What we need for Ideal final assembly of a radiant barrier system for Max R-value :

1. Horizontal installation: It simply means that we need the reflective surface lying horizontally. The further off horizontal we get the more we start creating convection currents as the heat rises along the surface of the radiant barrier, this dramatically reduces the final assembly R-value… In a hot tub, you have to install them vertically which is the worst case.
2. They need to maintain a specific gap between the reflective surface and the thing you are trying to insulate. The recommended gap is 1/2″ to 2″ On a hot tub, the distance between the reflective wrap and the hot tub ranges from 0 to 6″ so again nowhere near the requirements for good R-value for the final assembly.
3. If the reflective barrier touches the heat source (hot tub shell or pipes) it completely stops being an insulator at all and becomes a conductor!!! When they wrap the shell like they do at Hydropool the radiant barrier touches the pipes all around the spa creating tons of places that are not only not insulting at all but actually actively conducting the heat through the radiant barrier!!!
4. The reflective barrier needs to be sealed along all its edges. so again on a hot tub they would need to seal the radiant barrier to the shell at the top and the floor at the bottom sealing ai9r tight around the shell… this is not even possible and on that spa its not sealed at all which means the convection currents just cause the heat to rise and escape around the top of the radiant barrier.

Nobody uses this in the building industry anymore because it is simply not effective at containing heat in a system and the fact that some Hot Tub companies are now flogging this 3o-year-old tech as the next new hi-tech thing is in no way changing those facts.

Its cheap.


Glacier Bay Insulation Testing From:



Department of Commerce, BBB warn of salespeople pitching energy savings from radiant barriers. From:


Canadian mortgage housing corporation CMHC, From:


Glacier Bay Insulation Testing From:



Canadian mortgage housing corporation CMHC, From:



Green building advisor  From:


Reflectix Inc Installation manual N16 Revised 2011 from:


7.7 Total Score

Informative Article
Share Worthy
Would You Refer Chris?

Leave a Reply

Notify of

[…] insulation system is simply bad tech, all you have to do is a little bit of research on mylar and reflective installations and you’ll see that there’s just nothing good about these reflective insulation systems […]


Visitor Rating: 5 Stars

John Thomas

I just read your post regarding cal spa. I have owned a cal spa 5000 for 12 years now and every 2 years the main circuit board has needed replacing including right now also almost all the jet covers have broken off, i’m currently shopping for another brand spa. I live in michigan where the winters are cold. My question would be is Hydo pool or lazy boy something I should consider? My repair tech for the last 12 years has opened a store and is now carrying these brands?