What green and purple board actually are
Green board and purple board are paper-faced gypsum with moisture-resistant additives — not waterproof. Green board was the traditional “wet area” drywall; purple board (often branded Mold Tough or equivalent) adds mold inhibitors and tighter paper.
Both are fine on bathroom walls outside direct shower spray — vanity walls, toilet walls, ceilings. Neither belongs as the sole tile substrate inside a shower — use cement board or fiber-cement tile backer there.
- Shower/tub surround tile: cement or fiber-cement backer
- Bathroom walls outside shower: purple or green 1/2 inch
- Ceilings: same MR board or standard 1/2 inch per code
- Paint with bathroom-rated primer — board is not the finish
Code zones and practical layout
Many jurisdictions treat the shower interior as a wet zone requiring non-gypsum backer. The rest of the bath is “ damp ” — MR gypsum is acceptable when finished with tile or moisture-rated paint.
Plan sheet breaks at the shower curb or glass line so you do not mix backer and gypsum mid-field. Order MR board only for bath rooms — standard drywall elsewhere keeps costs down.
Estimating sheets for a bathroom
Measure each wall plane; MR board comes in same 4×8 and 4×12 sizes as standard. A typical 8×5 bath with 8 ft ceilings might need 6–8 sheets for walls plus 2–3 for ceiling before waste — less if a shower niche removes one full plane.
Enter room dimensions in our drywall calculator and note MR sheets on your pickup list separately from standard board.