This measurement will be from the top of the hot tub shell to the bottom edge of the shell or longer rounding up to the nearest inch.. This measurement is not from the top of the cover but from the bottom of the cover.. How to measure

Split corner skirts help prevent the skirt from folding under the cover when the cover is closed, allowing for heat loss. View

The only reason to order a thicker cover is if your tub is in a hole where people can step on the cover, or if you need more strength for sitting, snow, pets, etc.... The higher density foam does not really help with colder climates, so there is no reason to add the weight of a higher density foam unless you need the strength. View

R-value is the measure of the insulation value of the cover and 1.5lb 4-2 has as much insulation value as you would ever need so moving to the next thickness does not benefit you insulation wise contrary to what most manufacturers tell you.

Tapering Covers are thickest in the middle and slope outward like a roof
* Tapered covers are the most common and assist with rain run off
* Tapered covers are thickest across the fold and slope down to the sides with the handles
* We do not offer 1lb covers because they will not last. We offer two versions. The first is a 4-2 Taper 1.5lb standard cover which is adequate for most hot tubs or a 5-3 2lb version where you need more strength.

The life of your cover may be extended a year or more with an upgraded vapor barrier. 82% of covers eventually fail from waterlogging, the cause of the cover becoming heavy. The vapor barrier is the wrap around the foam cores, inside the cover, that keeps the moisture out.