Understanding Foam Density and Thickness

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Two primary choices consumers make when buying a spa cover center around the thickness and foam density. In general, a thick foam core offers greater insulation, and a denser foam adds strength. Let’s simplify that one more time – thickness equals insulation, and density makes a cover stronger, able to withstand more weight on top of it. If you’re interested in learning exactly what our cover foam cores are made of, you can check out the wiki on polystyrene. Polystyrene is also known as “EPS” or expanded polystyrene.

Two kinds of EPS foam exist. There’s one made form recycled foam beads, which are compressed and then glued together in sheets. Another type is made from “virgin” EPS. This foam comes in a sheet, which is heated, and expanded at the same time, resulting in a stronger foam core.

Our covers use the stronger virgin EPS cores for maximum durability. This foam density is measured in lbs/cubic feet, which allows you to judge how strong the cover will be.

The internal cores of hot tub covers are made from expanded polystyrene or EPS. We use virgin EPS only. The density of this foam is measured in pounds per cubic foot, and determines the strength of the spa cover.

To find the strength of some of our covers, refer to the list below. Keep in mind, these are “static” load measurements, such as the weight of snow evenly distributed across the cover. If your drunk mother in law decides to start dancing on the cover in her high heels, the pressure per square inch would be much more…and probably wouldn’t support her the same.

  • 4” to 2” taper with 1.0# foam              190 lbs
  • 4” to 2” taper with 1.5# foam              270 lbs
  • 4” to 2” taper with 2.0# foam              370 lbs
  • 6” to 4” taper with 1.5# foam              500 lbs

** Note: These are good estimates, taken for an 88″ x 88″ cover. A very wide cover will perform slightly different than a much smaller, narrower cover because the surface area is smaller.

Suppose Uncle Bill decides to dance a jig on your cover. In that case, we’re measuring a smaller footprint of pounds per square inch. Likewise, a dog weight on a spa cover is much different than the distributed weight of snow blanketing a cover

Shear – Strength Properties in pounds per square inch by density of foam

  • 1.0#       18 – 22 psi
  • 1.5#       26 – 32 psi
  • 2.0#       33 – 37 psi

Here are some real world examples:

  • If you live in a moderate climate that doesn’t receive much rain or snow, a 4″ – 2 tapered cover that’s under 84″ wide, the 4″-2″ tapered cover will work.
  • You live in a climate that sees some rain, snow, and mixed weather. The 5″-3″ tapered cover is the best choice, and you can add denser foam cores depending on the levels of rain/snow.
  • For those of you living in an area that gets a lot of snow or heavy rains, a 6″-4″ cover would suit you best. This cover will support a lot of weight, and remain well-insulated.

Remember, a thicker cover will add more strength than a thinner one too! Hopefully this helps clear up some of the confusion surrounding the strength and insulation of a cover and helps you make an educated decision.