This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Nap. [French naper, to nip off the knots on the surface of cloth] The wooly surface of felt, cloth aad plants. Specifically, the surface-covering of down or short fibers combed out of the substance of a fabric and all lying smoothly in one direction. The nap is the surface-covering of a fabric formed by teasling, the direction in which it lies always indicating the warp. From the nature of the surface of napped fabrics, as well as structure of the body of the cloth, they necessarily form very warm articles of clothing, the closeness of texture and the intermixing of the loose fibers of the nap all tending to assist in retaining warmth. [See Teas-ling]