We just got this solar cover yesterday, had it on the pool all day today. When I got home and checked the water the top six inches was hot like a hot tub. To me it seems to work much better than just the the ones that are just blue. The bubble side is black and it seems together a ton of heat. Granted it's a hundred degrees right now and Idaho and I'm sure that has something to do with it. I was going to let it double as a pool cover but I don't think I can do that now. I think in one or two more days I'm going to have a 6000 gallon hot tub.