Covering your hot tub when it is not in use can save you an incredible amount of money. In fact, most covers pay for themselves in just one season. A hot tub cover also protects your hot tub during the off season and can keep out human and animal intruders.

Almost all hot tub covers are made from EPS, expanded polystyrene. The insulating factor of this foam is in direct correlation to its density, or weight per cubic foot. Insulation is measured with an R factor, which refers to resistance to heat conduction. Most foam covers have a density between 1 and 2. A density of 1 provides 3.85 R, a density of 1.25 provides 4 R, a density of 1.5 provides 4.17 R and a density of 2 provides 4.35 R.

In addition to preventing heat loss from your filled hot tub, a cover should provide protection from snow and other weight during idle periods. That means it needs to be strong enough to withstand weight, yet light enough to easily lift on and off. Most hot tub covers are reinforced with aluminum or galvanized steel to support that weight, and to keep water from pooling in the cover. Also look for handles to make it easier to lift.

A locking mechanism can be a useful feature for a hot tub cover. That's partly a safety mechanism to keep children or animals out, and partly to hold the cover on in high winds. Finally, the bottom of the cover should have a chemical-resistant layer to extend the life of the cover.