Summer sheet for Horse Question?

I want to buy my mare a summer sheet to keep her clean during the hot summer months. I'm not looking for a fly sheet, but a full sheet that will act as a fly sheet as well. I found this a href="http://www.horse.com/item/kool-coat-classic-uv-fly-sheet/SLT900007/" rel="nofollow"http://www.horse.com/item/kool-coat-clas…/a and I'm not sure if it will work or not. I'm mainly concerned about her getting too hot in it, but I also live in california where there is little humidity when its hot out. I was wondering if anyone knew of more options or sheets like this one that would work well during the summer time. Also, my mare lives in a 2 acre pasture with 2 other horses, so she's always on turnout and no way to stall her. She is also mainly white so she usually keep a lot cooler then her pasture mates.