Thermal Resistance - Thicker vs Denser

Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater effectiveness of the insulation.

Put simply R-Values are a materials ability to resist the conduction of heat flow through a solid.

A hot tub has an R-value that represents the insulation in the shell and floor. The higher the R-Value, the slower heat passes through the shell to the outside.

Ensuring your hot tub has a good R-value will help greatly in conserving energy consumption.

An important factor in determining the R-value is the thickness of the foam. The R-value is determined by multiplying the R-value times the thickness. This is why thicker covers insulate better.

R-Value standards were developed for industries to follow which help consumers compare the R-Values of different types of insulation.


The maximum R Value obtainable for and Hot Tub Cover that is made with Expanded Polystyrene Insulation that is approved for sale in Canada is as follows:

Foam Thickness

1.5 LB foam / Type II (2) - Expanded Polystyrene Insulation

2.0 LB foam / Type IX (9) - Expanded Polystyrene Insulation


 R 4.55

 R 4.76


 R 9.10

 R 9.52


 R 13.65

 R 14.28


 R 18.20

 R 19.04


 R 22.75

 R 23.80


 R 27.306

 R 28.56

To help educate you for your next cover purchase, here is some background information:

  1. Hot Tub Manufacturers are only allowed to state the value of the insulation itself. In the case of hot tub covers, the R-Value advertised should only be for the insulating foam within the tub cover. Although it is true that the layer of polyurethane and the marine vinyl will increase the R-Value, it is not supposed to be included in the calculation.
  2. The R-Value of insulation increases when the air temperature on the cold side of the insulation decreases. So if you test insulation at 25°F and then at 10°F, you will get a higher R-Value at 10°F. Therefore the air temperature must be disclosed when an R-Value is stated. This helps consumers to make comparisons and also preserves the integrity of our industry.

Waterlogging also affects R-Values

A waterlogged cover will have almost no R-value, wasting your dollars on heating your hot tub.

When a tub cover becomes waterlogged it loses up to 75% of its original r-value.

One of the features of our hot tub covers is that we start with a 6 mil vapour barrier surrounding the foam, which completely encapsulates the insulation, and is both vacuum and heat-sealed. This provides a protective barrier to your cover to prevent water absorption, keeping your cover light over the years.

We highly recommend upgrading to include even more layers of vapour barrier as it is a small investment for the additional years your cover will remain highly efficient, light and easy to handle.

hot tub cover hinge sealWe also offer a Full Hinge Seal upgrade to protect your spa cover from heat loss which occurs from the center seam of a cover. Without this useful extra seal, it is like having a 3/4" gap down the centre of your hinge between the steam pockets.

Let's say your hot tub cover is 84" x 84" - Your cover would have 80 *.75" = 60 square inches of the gap. This is equivalent to the size of a 6" x 10" square.

We recommend purchasing this upgrade when ordering your custom hot tub cover in our Build a Cover process.

This helps prolong your spa's life (and warranty protection!) and protect your hot tub cover against moisture/water absorption that will reduce the R-value of your hot tub - which doesn’t reflect well on the monthly energy bill!

And always make sure your hot tub cover straps are secure, otherwise your efforts to protect against waterlogging may be in vain.

For further cover care tips to protect help against waterlogging, read our article Caring for Your Hot Tub Cover »

additional hot tub cover upgrades and optionshow to measure for replacement hot tub covercreate hot tub cover template3 times the amount of vapour barrier protection
comparison chart of our spa covers vs the competition