Definition (Source: Wikipedia)
***Drywall, also commonly known as gypsum board, plasterboard (UK, Ireland, Australia), Gibraltar board or gib (New Zealand - GIB being a trademark of Winstone Wallboards), rock lath, sheetrock (a trademark of United States Gypsum Company),[1] gyprock (Canada and Australia - likely a portmanteau of "gypsum board" and "sheetrock" also a trademark of CSR Building products Australia), or rigips (Germany and Eastern Europe - after the Rigips brand) is a common manufactured building material used globally for the finish construction of interior walls and ceilings. Drywall is typically available in 4 ft (1219 mm) wide sheets of various lengths. With the rising popularity of 9 ft. high ceilings in new home construction, 54" wide panels have become commonly available as well. Newly formed sheets are cut from a belt, the result of a continuous manufacturing process. In some commercial applications, sheets up to 16 ft are used. Larger sheets make for faster installation, since they reduce the number of joints that must be finished. Often, a sizable quantity of any custom length may be ordered, from factories, to exactly fit ceiling-to-floor on a large project.
The most commonly used drywall is one-half-inch thick but can range from one quarter (6.35 mm) to one inch (25 mm). For soundproofing or fire resistance, two layers of drywall are sometimes laid at right angles to each other. In North America, five-eighths-inch-thick drywall with a one-hour fire-resistance rating is often used where fire resistance is desired.
Drywall provides a thermal resistance R-value of 0.32 for three-eighths-inch board, 0.45 for half inch, 0.56 for five-eighths inch and 0.83 for one-inch board. In addition to increased R-value, thicker drywall has a higher sound transmission class.