It is the same as regular drywall except for two things:
- Its paper covering resists water (but is not water-proof).
- This paper is green. The color imparts no special water-resisting properties, but it does help the installer better see where he/she is applying the drywall compound.
Materials and SizingThe gypsum material sandwiched between two paper coverings is the same. Also, whereas regular drywall comes in 1/4" and 1/2" sizes, greenboard drywall comes in 1/2" and 5/8" sizes. Greenboard goes by various brand names, such as American Gypsum's Aquabloc.
For Damp, But Not Wet, ApplicationsThis is a common misunderstanding. While greenboard drywall's paper covering is water-resistant, it is not waterproof. Not only that, but the brittle gypsum core is not suitable for wet applications. A cement-based backerboard like Wonderboard or Hardibacker is suitable for tile-covered wet applications like showers and tub surrounds.
Instead, greenboard is used in bathrooms, basements, and other areas where the drywall may be subjected to damp conditions, humidity, and the occasional minor splashes of water. Using greenboard drywall in a wet location is a recipe for disaster. At the very least, severe mold growth will occur, if not outright failure of the product.