I honestly don't think I could say enough good things about this sleep sack. We live in Florida and our summers are so hot our a/c has trouble keeping up and we only set it at 74. Adding to that, my son is heat sensitive and we were having a major problem with heat rash developing overnight with his regular sleep sacks (cotton Halo brand sleep sacks), and a hot baby at night is not good. I already had experience with the awesomeness that is wool because we use wool shorties as our cloth diaper covers so I was expecting good things already.I was worried about the price but knowing that I've spent that and possibly more over the last year and a half or so on sleep sacks I figured it couldn't hurt to give it try. I am so happy I did. The quality of the construction is phenomenal. The seams are tight, the zipper glides smoothly and the snaps are solid. It has a cotton outside and a wool inside that is incredibly soft even after washing. The sack itself feels heavy so I was a little cautious at whether or not it was too heavy and would not keep my son cool enough but I was happily proven wrong. After the first night the heat rash we had been battling was now almost non existent (it is currently completely gone and has stayed that way) and he slept more restfully through the night without the 5:45am wake ups we had been going through for a few weeks.This sleep sack has been a lifesaver and I wish I had purchased one sooner but I know with the next baby I will be using these as soon as it fits.