Glass-fiber insulation in board or blanket form is used in several applications for airborne and impact noise isolation in residential construction. These include (1) sound-absorbing cavity fill for improving the airborne transmission loss of walls and floors, (2) vibration-isolating underlayment in floors and single-stud walls, and (3) finished acoustical materials for absorption of reverberant room noise. The improvement in transmission loss of a wood-stud drywall due to a 3-in. thickness of glass-fiber cavity fill ranges typically from 2 to 10 STC, depending on the degree of structural isolation between the two sides. The improvement is found to increase with thickness of cavity fill, but is virtually independent of density or flow resistance over a wide range. In steel-stud drywalls, glass-fiber board applied between the gypsum board and the stud acts both as a vibration isolator and sound absorber. Improvements of 10 STC are typical. In hard-surfaced wood joist floors, a combination of glass-fiber-board underlayment, blanket cavity fill, and a resiliently supported ceiling yields an over-all improvement of 16 in Impact Noise Rating.