I purchased this sleep sack for my son before winter and he's worn it all winter for naps and bedtime. His room has old, drafty windows so it gets a little chillier than the main part of the house. I don't have any worry about him getting cold in this. He always wakes up toasty warm and he only wears this two piece pajamas underneath it. It's been washed so many times in the past few months and has no flaws at all.