As quiltingshorttimer said, Poly or wool. But I disagree on the poly doesn't breath. I have two bed quilts I use regularly that have poly. One was hand quilted and the other machine quilted. The hand quilted one I can actually feel the breeze of my ceiling fan through if it is the only covering on me. The machine quilted one is also not too hot. So these two are my primary summer quilts. But I do layer them up in the winter with a quilt batted with 80/20 and on those really cold nights the down comforter gets use as well. I find I overheat more when sleeping under the quilt done with 80/20 batting. This is just my experience.
Other advantages to poly, it dries quickly, doesn't hold wrinkles, is much less expensive than wool and can be used when someone has wool allergies. It also softens up and gets better drape with use.