36 x thick with open (untaped) edges.

Gypsum board evolved between 1910 and 1930, beginning with wrapped board edges and the elimination of the two inner layers of felt paper in favor of paper-based facings. In 1910 United States Gypsum Corporation bought Sackett Plaster Board Company and by 1917 introduced Sheetrock. Providing installation efficiency, it was developed additionally as a measure of fire resistance. Later air entrainment technology made boards