We bought this originally for a 15' easy set pool at the beginning of the summer and we're still using the same one after upgrading to an 18' pipe frame pool. It made a DRASTIC difference in both heating speed and maximum temperature of our pool water, in both cases. The most important thing is putting the cover back on when you aren't using it, because it starts heating the water as soon as the sun starts coming up in the morning and any level of light is passing through the little bubbles in the cover, even when the air doesn't feel warm on your skin yet, and it also insulates the surface of the water from evaporation and from getting chilled by the cold air (like at night).It was a little too big for the easy set pool, since the top inflatable ring isn't actually the full 15' that the lower liner part fills out to (which is what the pool is labelled based on so it sounds bigger when you're buying it), it's really more like 13', maybe 13.5'. This caused excess material to stick up over the inflatable part, which at first we thought couldn't hurt...it'll just keep debris from getting into the water along the edges, right? Except the part sticking up around the edges would catch the breeze, which sometimes meant we'd find it on the ground when we came outside, and one time a strong wind blew the cover partially off so it was hanging over one side of the pool enough that the weight of it caused that side to collapse and dump 1000-ish gallons of water all over our patio before we caught it. When we didn't have to worry that it might be getting too windy though, it was AWESOME. Our hose water comes out of the well at 54 degrees and that cover raised it to 70 in one full day of sunshine (on not even that hot of a day, like 75 , I live in Oregon) and then reached 81 by day 3 and maintained it even though it goes down to 50 at night in the summer here. If you're looking into getting a solar cover for an easy set pool I would say DO buy one, but get the next size smaller than your pool to make up for the taper in at the top. It's VERY important that this cover is laying flat across the surface of the water and not curving up the side of your pool at all to maintain the surface tension and avoid turning the cover into a sail and/or causing a patio flood.Since upgrading to the bigger pool, it still works GREAT. Sure, this 15 footer doesn't cover the entire surface of the 18' pool, but it still heats the water, and with the new pool being a darker color (a brown wicker pattern compared to the lighter blue of the old easy set pool) it seems to absorb enough extra sun on its own to still sit around 80-82. When it's time for a replacement solar cover due to normal wear & tear I'll probably go ahead and order the bigger one to match the new pool (and I'm assuming at that time I can just get an 18' one since the pipe-frame pool has straight vertical sidewalls instead of tapering like the easy set) but this works well enough to not bother buying another until then.