Terms of the Trade: What Is Greenboard?
When constructing a bathroom or other area such as a basement or utility room with damp conditions, you should use a moisture-resistant board—such as greenboard—instead of standard drywall. While both drywall and greenboard are made of gypsum, greenboard's paper covering is water-resistant, and the board is slightly thicker than standard drywall. While unique, the green color exists only to distinguish it from other boards. (Note that greenboard is not water-proof. It shouldn't be used in shower construction—use cement backer board for that.)