Drywall, also called gypsum board or wallboard, is a common interior finish providing fire protection, soundproofing, and a smooth surface for decoration. Drywall consists of gypsum plaster sandwiched between paper layers. Common thicknesses are 3/8, 1/2, and 5/8 inches; 5/8-inch board provides better fire and sound performance. Installation involves fastening boards to studs or joists with nails or screws. Screw fastening is preferred as screws hold better than nails. Fastener spacing of 16 inches on center along supports is typical. Boards are cut and fitted around windows, doors, and penetrations. Joints between boards are taped and finished with joint compound (mud) to create a smooth surface. Taping involves embedding paper tape in joint compound, then adding additional coats of compound and sanding smooth. Multiple coats (typically 3 to 5) create a finish suitable for painting. Fastener heads must be covered with joint compound. Corner beads provide reinforcement at inside and outside corners. Fire-rated drywall assemblies achieve fire ratings through board thickness, material type, and fastening. Type X gypsum board has additives improving fire resistance. Type C has enhanced fire performance for special applications. Soundproofing improves with thicker boards, multiple layers, and resilient channels reducing vibration transmission. Moisture-resistant (green) drywall is used in bathrooms and other wet areas. Moisture resistance prevents moisture absorption that would cause deterioration. Mold-resistant (purple) drywall is available for additional protection. Finishing quality depends on taper and smoothness; poor finishing is visible under paint or wallpaper.