Regular Drywall
Standard drywall (also called whiteboard or regular gypsum board) has no moisture resistance. The paper facing absorbs water readily and the gypsum core breaks down when wet. In a bathroom that gets humid during showers, regular drywall on the walls will eventually fail — the paper delaminates, the gypsum crumbles, and mold grows behind the surface where you can't see it.
The only place standard drywall belongs in a bathroom is the ceiling, and even then, only if it's at least 6-8 feet from any direct shower spray. For ceilings directly over a tub or shower, use moisture-resistant or, better, cement board.
Cost: typically $8-10 per 4x8 sheet in 1/2-inch thickness.
Moisture-Resistant Drywall (Green Board)
Green board uses wax-treated paper and a moisture-resistant gypsum core. It handles humidity much better than standard drywall — a bathroom that steams up daily won't damage it the way it would regular board. Green board has been used in bathrooms since the 1960s.
The critical limitation: green board is not waterproof. It resists moisture in the air; it does not withstand direct water contact. Behind a tile installation that gets wet repeatedly — shower walls, tub surrounds — green board will eventually fail. Water migrates through grout and tile over time, especially as grout ages and develops hairline cracks. Green board cannot handle this long-term exposure.
Where green board is appropriate: walls in bathrooms that don't have tile or direct water spray. Behind a vanity, on walls opposite the shower, in laundry rooms, on garage walls prone to condensation.
Cost: typically $10-12 per 4x8 sheet in 1/2-inch thickness.
Cement Board
Cement board (USG Durock, James Hardie Backer, Permabase) is made from portland cement and aggregate reinforced with fiberglass mesh. It has no paper facing and no organic content — there's nothing for mold to eat and nothing to deteriorate when wet.
Cement board is the correct backing for tile in direct water areas: shower walls, tub surrounds, shower pan areas, and anywhere tile is installed where water regularly contacts the surface. The International Residential Code (Section R702.4) requires a "water-resistant gypsum backer board or other equivalent material" behind tiled shower walls — cement board satisfies this requirement; standard green board typically does not meet the code requirement for tiled wet areas in most jurisdictions.
Downsides: heavier than drywall (a 1/2-inch 3x5 sheet weighs around 45 lbs vs. 28 lbs for drywall), harder to cut (score and snap works but takes more force, and a carbide blade extends saw blade life significantly), and it requires fiberglass mesh tape rather than paper tape at seams. Alkaline-resistant mesh tape is recommended because cement is alkaline and will degrade standard fiberglass mesh over time.
Cost: typically $14-18 per 4x8 sheet in 1/2-inch thickness.
Comparison by Use Case
The quickest way to make the decision:
Shower walls (tiled): Cement board. Not green board, not regular drywall.
Tub surround (tiled): Cement board.
Bathroom walls not near water: Green board or regular drywall.
Bathroom ceiling over shower: Moisture-resistant drywall or cement board.
Laundry room walls: Green board.
Basement walls prone to condensation: Cement board or moisture-resistant drywall.
Kitchen backsplash area (tiled): Regular drywall is fine — kitchens don't generate the sustained moisture that bathrooms do.
One additional consideration: some tile manufacturers void their warranties if their tiles are installed over green board in wet areas. If that matters to you, check the tile warranty before you frame out the backing.
Cost and Labor Comparison
For a typical 5x8 bathroom shower surround (roughly three walls, approximately 60 square feet of wall surface), here's a rough comparison:
Standard drywall: ~$15 in materials. Wrong choice, but cheapest upfront.
Green board: ~$18 in materials. Wrong choice for tiled shower walls, but a marginal cost difference.
Cement board: ~$35-45 in materials. Correct choice for tiled shower applications.
The labor difference between installing green board and cement board is minor — maybe an extra 30 minutes for a bathroom-sized project due to the heavier weight and harder cutting. The $20-30 material premium for cement board is insignificant against the cost of a mold remediation or tile re-installation project four years down the road. Those run $2,000-5,000 depending on the extent of the damage.