I tried this for the first time when I went on vacation with my daughter. She sleeps in sleep sacks at home but sometimes she sweats in her organic cotton sleepsack. However, I haven't felt her sweat in this sleep sack nor the winter-weight version of this sleep sack. The material feels very soft and smooth and seems very comfortable. My daughter is only 1.5 years old and there is still lots of room for her to grow.