Flannel

Flannel's defining characteristic — its soft brushed surface — is a finishing process applied after weaving: the fabric is passed over rotating wire-covered rollers (a napper) that raise and partially break short fiber ends from the yarn surface, creating a fibrous nap layer. This nap traps a thin insulating air layer next to skin, raising the fabric's thermal resistance significantly compared to an unbrushed fabric of the same weight. Cotton flannel is typically woven at 3–5 oz/yd² in plain or 2/1 twill and napped on one or both sides; double-napped flannel has greater insulation but loses more strength over time as the napping shortens fiber length. Brushed wovens are vulnerable to pilling where the raised fibers re-entangle under friction, particularly at collar, cuff, and underarm contact points. Quality flannel uses long-staple combed cotton or a cotton-wool blend; budget versions use carded cotton whose shorter fibers produce denser but less durable nap.