My friend has a habit of waking up sweaty in the middle of the night. We've tried a variety of down and cotton duvets in various weights and styles, but nothing seems to keep him as cool as a flat sheet.

We've been looking into bamboo comforter set and silk duvets because he prefers to sleep with a comforter. I'm curious if one is better for cooling than the other. I discovered a 175GSM silk duvet, but there have been varied opinions on silk's ability to retain heat versus wicking, so I'm not sure if bamboo would be a better alternative.