I only use polyester batting, it doesn't shrink like cotton will and warm and natural shrinks also. All 92 Quilts and comforters I have made in the last 45 years has polyester batting inside them.
It is very nice to work with. I used warm and natural in a bird cage cover and it shrank when I washed it and dried it, polyester has never done that. We sleep under a quilt all year round and have no problems, heat in winter and A/C and ceiling fan in summer.