National Gypsum Permabase or USG Durock 

• Rigid substrate made of Portland cement, aggregate and fiberglass mesh.
• Suited as underlayment for tub and shower surrounds, countertops, flooring and other interior and exterior applications.
• Highly moisture resistant. Will not rot, disintegrate or swell when exposed to water.
• 30-year limited warranty on interior applications. 10-year limited warranty on exterior applications.
• Cut with utility knife and straight edge.
  • Stock:
    • 1/2" 3x5

HardieBacker 

• 90% Portland cement and ground sand. Contains no asbestos, glass mesh, formaldehyde, or gypsum.
• Lightest cement board available. Cuts easily.
• Features exclusive EZ Grid recessed fastener pattern to make installation easier.
• Provides superior protection agains moisture damage and mold growth.
• Non-combustible.
• Limited lifetime product warranty.
  • Stock:
    • 1/4" 3x5