Drywall (also known as plasterboard, wallboard, gypsum panel, sheet rock, or gypsum board) is a panel made of calcium sulfate dihydrate (gypsum) with or without additives and normally pressed between a facer and a backer (typically thick sheets of paper). It is used to make interior walls and ceilings. The plaster is mixed with fibre (typically paper and/or fibreglass), plasticizer, foaming agent, and various additives that can decrease mildew, increase fire resistance, and lower water absorption.