As mentioned, PCMs in the gel memory foam work by absorbing excess heat from the body, releasing that stored heat, and adapting to the environment temperature. For example, when you’ve been lying on a gel memory foam mattress for a while, it will feel soft and warm under your body heat. The foam will stiff up again and adjust to room temperature when you get out of bed. These gels are similar to gel packs on freezers. So if it gets cold in your room in the winter, your gel mattress can also get cold. If this is the case, you can use thick blankets alive your mattress for a more comfortable sleeper surface in the winter.