blanket insulation

Blanket insulation is a flexible, compressible mat of glass fiber, mineral wool, or polyester that comes in rolls and is installed by unrolling it between studs, joists, or rafters. It is the most common form of thermal insulation in residential and light commercial construction because it is cheap, quick to install, and requires no special equipment beyond a utility knife and staple gun. A typical roll covers 50 to 80 square feet and weighs 5 to 15 pounds depending on thickness and density.

Blanket insulation is sold in standard widths of 16 or 24 inches to fit cavity spacing, and thicknesses range from 2 inches (R-7 to R-8) to 10 inches (R-38 to R-40). Glass fiber batts are the baseline: inexpensive, non-combustible, and widely available. Mineral wool batts offer better fire and sound resistance but cost more. Polyester batts handle moisture better in humid climates. The facing, if present, is either kraft paper or foil, serving as a vapor retarder when installed on the warm side of the cavity.

Installation faults are common and reduce performance significantly. Gaps around electrical boxes, pipes, and band joists allow air leakage. Compression reduces R-value: stuffing R-19 fiberglass into a 2-inch cavity drops its rating below R-13. Moisture trapped behind an improperly placed vapor retarder causes mold and fiber degradation. Building wrapping also matters: unsealed air leaks in the wall or ceiling assembly can make an R-20 installation perform like R-10.

Unfaced batts have no barrier and are used for interior cavities or when another vapor control method is present. Faced batts have kraft or foil backing and go closest to the conditioned space. High-density fiberglass (denser than standard batts) improves fire rating and air-tightness. Some products include recycled content or formaldehyde-free binders. Fiberglass remains the majority due to cost; mineral wool is chosen for fire-rated assemblies or where noise control is critical.

Blanket insulation sits below rigid boards and spray foam in terms of thermal performance per inch but above blown-in fiber in ease of retrofit. It requires a cavity to fill, so uninsulated concrete slabs and solid masonry need different approaches. Batts have fallen slightly in market share since 1990 as spray foam and blown cellulose have become more affordable, but they remain the default choice for new framed construction because installation labor is minimal and the material cost is lowest on a per-R-value basis.