I don’t yet have a hot tub but if I did I would certainly want one of these solar powered spa heating covers. Not only is it good for your spa but it’s nice to look out. Especially if you have an addiction to celestial sun and mood items like myself ;)

“This spa cover uses two layers of durable UV-resistant vinyl that use solar energy to heat your outdoor whirlpool or spa, and it reduces water and your spas chemicals less through evaporation. The transparent upper layer of vinyl focuses sunlight onto the lower translucent blue layer, which absorbs 50% of incoming sunlight, converting it to heat. The remaining balance of the sunlight passes through the translucent layer for deep water heating. ”

Source.