Traditional memory foam mattresses are known for motion separation and pressure relief. Unfortunately, they're also known for a sinking, hard-to-move sensation and heat build-up. That's why Simmons has created a superior memory foam. NXG Memory Foam And Comforpedic Advanced NxG® Memory Foam not only responds quickly to your movements, but also dissipates heat to help keep you at your ideal sleeping temperature.The result is a mattress that provides the ideal combination of comfort and support without feeling like you're sleeping in quicksand.