Drywall is a common building material that is used to create walls and ceilings. It is made of gypsum plaster that is sandwiched between two sheets of paper. Drywall is porous, which means that it can absorb moisture from the air. This can lead to the growth of mold, which can cause health problems for occupants. To prevent mold growth, it is important to keep drywall dry. The normal moisture reading for drywall is below 16%.