1.1 This specification covers fibrous glass insulation used as a thermal and sound absorbing liner for interior surfaces of ducts, plenums, and other air handling equipment that handle air up to 250°F This specification covers fibrous glass insulation used as a thermal and sound absorbing liner for interior surfaces of ducts, plenums, and other air handling equipment. The insulation shall be of the following types: Type I and Type II. The basic mate