I'm sure by now everyone has seen these inflatable circles touted as "Solar Sun Rings" which make all sorts of claims to keep the heat in your pool from evaporating off the surface (My most recent favorite: "PROVIDE 21,000 BTU’S OF HEAT PER RING, PER DAY – FOR FREE!" "Extend your swimming season and slash your energy bills with In the Swim's innovative Solar Sun rings. Solar pool sun rings are vinyl discs which lie on the surface of your swimming pool and use heat energy from the sun to raise the temperature of your pool. More specifically, the upper clear layer of solar sun rings holds insulating air and also focuses sunlight on the lower blue layer of the discs. The blue layer of swimming pool solar sun rings absorbs approximately 50% of sunlight and converts it to heat, while allowing the remaining sunlight to pass into the pool for deep water heating." Ummmm.....while I would love keep more of the heat that I put in my pool, well, in my pool, I simply can't believe that these things actually work. Especially on a free form pool with a raised attached spa.