Term Description
Asbestos felt

See ‚"felt.‚"

Asphalt felt

An asphalt-saturated and/or asphalt-coated felt. See "felt."

Coated felt (sheet)

(1) An asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) a fiberglass felt that has been simultaneously impregnated and coated with asphalt on both sides.

Dry-in (or dry-in felt)

Usually the underlayment or the process of applying the underlayment for steep-slope roofing. In low-slope roofing, it is usually called a temporary roof.


A flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture and heat. Felts are manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (fiberglass felts or ply sheets) or polyester fibers; other fibers may be present in each type.

Fiberglass felt

See "felt."

Glass felt

Glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roof membranes and shingles.

Organic felt

An asphalt roofing base material manufactured from cellulose fibers. See "felt."

Perforated felt

Bitumen-saturated felt perforated with closely spaced small holes to allow air and moisture to escape during application of built-up roofing; depending on the type of material or specific use, can be classified in accordance with ASTM D226, D2626 or D4897 requirements.

Saturated felt

A felt that has been immersed in hot bitumen; the felt adsorbs as much bitumen as it can retain under the processing conditions but remains porous and contains voids.

Strapping (felts)

A method of installing roofing rolls or sheet good materials parallel with the slope of the roof.