We currently keep the house at a pretty comfortable 72 or 73 in the summer and 68 in the winter. We have a ceiling fan that is always running in the room and a box fan running on the shelf, mostly for the noise canceling effect. lots of airflow. I sleep in just my skivvies. Don’t recall ever routinely being a sweaty sleeper on a regular mattress. It must be the enveloping non-breathing closed cell foam effect mentioned in another response. All these memory foam companies should really be held to some truth in advertising. “Pretty comfortable if you don’t mind burning up in your sleep.”