mattress pad(n = noun.artifact) - a protective pad over a mattress to protect it;
is a kind of pad

air mattress, arm pad, body pad, brake pad, carpet pad, cleaning pad, elbow pad, heating pad, hip pad, hot pad, inking pad, knee pad, launch pad, launching pad, lily pad, mattress, mattress cover, message pad, pad, pad elephant, pad of paper, rug pad, scouring pad, scratch pad, sea pad, shoulder pad, sketch pad, soap pad, spring mattress, stamp pad, steel-wool pad, thigh pad, wrist pad, writing pad