What causes the underside of some covers to sag and droop into the water?
Besides the obvious reason of a loosely fitted vinyl covering, the frequent cause of sagging is excessive air inside the polyethylene that seals the foam cores. Manufactured at cool temperatures, once on your spa the additional heat of the water will cause any trapped air in a cover to expand. It’s important (though difficult) to vacuum out any air that might be trapped during the process of sealing the foam cores in the polyethylene.
