Everyone's body temp will be different and no duvet insert will work for 100% of people. With that said, I feel like this insert will work for atleast 75% of people, and I say that because my wife sleep cool and I sleep on the warm side, and this insert works for both of us. Add to the fact that it has corner ties, and you have a real winner.
1) Perfect temperature (I feel this is probably 90% of the review in and of itself)
2) Perfect amount of fill. Not too thin, and not too overly thick.
3) We end up with a good 6-8" of extra material on each side so those with tall bed's should be OK.
4) Both of our cat's love it!