Johns Manville Formaldehyde-Free™ Fiberglass Insulation (Specific for 2" x 8" WOOD framed walls with joists spaced 15" apart) R-Value: 28 Dimensions: 8½" x 15" Coverage: 40.0 sq. ft./bag Application: Attics JM Formaldehyde-Free™ fiberglass insulation promotes better indoor air quality, provides superior thermal efficiency and a reduction in sound. Data Sheet