I was so glad to finally get a sleep sac that comes with clear instructions on how to get your baby to the right temperature. I was losing sleep over it! Unfortunately, I am still losing sleep over it as the wool layer is super thin and my baby wakes up with chilly face and arms/hands, sometimes feet too. I'm told this is actually how you want babies to be, so long as their core is warm, which it is. However, if I were wearing the sac I'd be freezing all night.... I do like that these breathe. We use it with shot sleeve onesie + long sleeve flanel onesie pjs at 63-69F room (unfortunately that's as steady as we can get it). One bonus is these actually have room for her legs, as she's in 99th percentile height at 3 months.  But they're so long that it's a hike to get the entire thing into the crib with her. I do wish the colors/patterns were a bit cuter as the stripes are a bit too adult for baby. She looks like she's wearing a little kimono. I also wish they could go in the drier as it takes a while for them to dry. I read somewhere that these were three layers, but what I receive dare just two (thin soft wool on inside, soft cotton on outside).