The terms mattress topper, mattress overlay and mattress pad are often thought to mean the same thing. The terms mattress topper or mattress overlay refer to something that enhances the comfort level of the mattress by adding an extra soft layer, pad, or overlay on top of an existing, and possibly too hard mattress.The term mattress pad can refer to both a mattress topper, and to a thinner pad made out of cotton or polyester which is put on top of a mattress to protect it. These mattress pads are also known as mattress protectors.