It might be a little hotter, but not much, it's pretty thin. I quilt mine too, just by running extra lines of stitches from front to back to give it some more stiffness. There's no batting in between, just rows of stitches holding the 2 pieces of fabric together. You can see it better in this pic...
I hose the horse off in summer before loading him into the trailer to go...
My problem with that is that most of the places I ride require that I drive the last 8 or 10 miles (at least) on dirt roads, and with an open trailer, well, you have a dust colored horse when you get there. By the time we finish riding, there are actual rivers of mud pouring out of the horse's hair. It's really gross.