Best Latex Mattress Toppers of 2026 - Sleep Foundation A mattress topper is an extra layer that rests on top of the existing mattress to finetune its feel Most toppers measure 1 to 3 inches thick, and they can make the bed feel plusher or firmer depending on the thickness and firmness of the topper and the feel of your existing bed While toppers come in many different materials, latex toppers are especially popular for their temperature control