US Patent 8734613 Glass fiber enhanced mineral wool based acoustical tile

A wet laid basemat for an acoustical ceiling tile comprising on a dry weight basis, 50% or more mineral wool fiber, including shot, less than 9% binder, and between 5 and 20% chopped strand glass fiber, and, optionally, minor amounts of other constituents, whereby the chopped strand glass fibers serve to promote and/or maintain voids in the mat such that the dry basemat has a density of between about 7½ to about 10½ lbs. per cubic foot and an NRC substantially greater than 0.55.