I’ve never had that issue personally. Even before I had air conditioning, this wasn’t an issue for me in the summer. However, I don’t doubt that a memory foam m

I’ve never had that issue personally. Even before I had air conditioning, this wasn’t an issue for me in the summer. However, I don’t doubt that a memory foam mattress is warmer than a traditional mattress so I can totally understand that this could be a factor for others. I wonder if other foam mattresses are any different in this respect. On the topic of thermal mass, more thermal mass would actually keep you cooler longer, because it would take longer to saturate the mattress with heat. Ventilation is probably a much more significant issue than thermal mass though.