Green Board
The original moisture-resistant drywall. Green board has been around for decades and is what most people think of when they hear moisture-resistant drywall.
The difference from regular drywall is the paper facing. Green board's paper is treated to resist moisture absorption. Regular paper facing acts like a sponge for water. The treated paper doesn't absorb as readily.
Cost is typically $2-4 more per sheet than regular drywall. Handles the same as regular drywall for installation.
Use it for: Bathroom walls and ceilings away from direct water, kitchen walls, laundry rooms, any area with higher humidity than typical living spaces.
Don't use it for: Shower and tub enclosures where water contacts the wall directly. Green board will eventually fail under constant moisture. These areas need cement board or similar.
I used green board on our bathroom walls, but cement board inside the shower. Three years later, the green board areas look perfect.
Purple Board and Mold-Resistant Drywall
Purple board, most commonly from National Gypsum, is a step up from green board. Other manufacturers make similar products with different colors, but purple has become almost generic for this category.
The difference from green board: purple board doesn't just resist moisture absorption, it actively inhibits mold growth. The gypsum core is treated in addition to the paper facing. Even if moisture does get in, mold has trouble colonizing.
Cost is about $5-8 more per sheet than regular drywall. Still installs the same way.
Use it for: Same applications as green board, especially in high-humidity environments. Good choice for basement finishing, bathroom ceilings, or anywhere you've had mold problems in the past.
I upgraded to purple board for our bathroom ceiling after discovering the previous exhaust fan wasn't venting properly. Years of humidity had caused mold issues. The purple board, combined with a properly vented fan, has stayed mold-free.
Paperless Drywall
Takes a completely different approach. Instead of treating the paper to resist moisture, it eliminates the paper entirely. Fiberglass mat covers the gypsum core instead.
Why this matters: paper is organic material. It's food for mold. No paper means no mold food. The fiberglass facing is inorganic and can't support mold growth.
Cost is significantly higher, often $15-20 more per sheet than regular drywall. It also finishes slightly differently since the fiberglass texture isn't identical to paper texture.
Use it for: High-moisture environments where you want maximum mold protection. Basement finishing. Commercial kitchens. Anywhere you're very concerned about mold.
I haven't used paperless drywall personally, but my brother installed it in his finished basement after dealing with recurring moisture issues. He says it's held up well over five years.
Cement Board and Tile Backer
Not technically drywall, but it's what goes where drywall can't. Inside showers, tub surrounds, and anywhere that sees direct, repeated water contact.
Cement board is Portland cement with fiberglass mesh. Water literally cannot hurt it. You can soak it, spray it continuously, it doesn't care.
Products like Durock, Hardiebacker, and Wonderboard are the standards. Alternative products like Kerdi board and GoBoard combine backer with waterproofing membrane.
Cost is more than drywall, and it's heavier and messier to cut. But it's the only appropriate substrate for tile in wet areas.
The key point: no drywall, regardless of moisture resistance, belongs inside a shower or tub enclosure. Green, purple, paperless, none of them are meant for direct water contact. That's cement board territory.
Making the Choice
My decision process for moisture areas:
Direct water contact (showers, tub surrounds): Cement board. No exceptions.
High humidity bathroom areas (ceilings, walls near shower): Purple or mold-resistant drywall. The extra cost is worth the peace of mind.
Standard bathrooms, kitchens, laundry: Green board is adequate. It's the minimum I'd use in any wet space.
Basements: Mold-resistant or paperless. Basements have inherent moisture issues. Go with stronger protection.
The price differences are small compared to the cost of dealing with mold or moisture damage. A bathroom with maybe 200 square feet of wall and ceiling costs about $50 more to do in purple board versus green board, and maybe $100 more versus regular drywall. That's cheap insurance.
Ventilation Matters More
Here's what I've learned: the type of drywall matters less than proper ventilation. A well-ventilated bathroom with regular drywall will outperform a poorly ventilated bathroom with the best mold-resistant drywall.
The exhaust fan is crucial. It should run during showers and for 15-20 minutes after. It should actually vent outside, not into the attic. And it should be sized for the bathroom.
I found out our bathroom fan was dumping into the attic space instead of outside. All that humidity was going straight into the insulation. Fixed the venting, and the humidity issues improved dramatically regardless of drywall type.
Use moisture-resistant products as part of an overall moisture management approach, not as a substitute for proper ventilation.