fiberglass batts
Flexible sheets, pads, or bags of glass fibers used as thermal insulation, with or without a facing.
Fiberglass batts are sheets, pads, or bags of low- to high-density glass fibers. This is an extremely common form of insulation, especially in homes. Handling can release fibers that temporarily irritate the skin, eyes, or respiratory tract. The glass fibers are noncombustible, but kraft-paper and some foil facings can burn. Facings can also serve as vapor retarders.
The fibers form a flexible mass that holds together as a batt. Loose-fill insulation instead consists of material placed without that integrated batt form.
A facing can provide vapor resistance while having different fire properties from the glass fibers. Unfaced insulation and a faced product therefore do not necessarily have the same combustibility.