All memory foam mattresses, including those designed to stay cool, can still retain some heat. Heating throughout the night has been a common problem since memory foam was first introduced; however, brands address this by adding extra materials to keep their memory foam cool, such as copper and graphite. There is also a potential of sagging in memory foam, especially at the edges (where people enter and exit the bed). However, most of these mattresses now come with reinforced edges to help this issue.