[herf]

I avoid all "cooling foam" or "gel foam" as it has a relatively fixed capacity to absorb heat. In other words, it seems cold in the store and also for the first few hours of the night. But after it does its phase-change magic, it gets dramatically hotter and can wake you up around the time cortisol starts increasing like 3-4AM.

[bityard]

Can confirm... I have a foam mattress that claims to have the fancy cooling stuff built in. It's actually all-around fine in the summer when the temps are 75F inside and I can sleep with few/no blankets, but I live in the Midwest and the house thermostat is set to heat up to 65F for 2/3 of the year. For the first 15 minutes, it's like crawling into a very soft refrigerator. And a few hours later, I'll wake up dehydrated and soaked in sweat.

I've managed to mostly tame it by putting a quilt or two under the bottom sheet.