Flannel is recognised for a soft textile character and can be made with cotton, wool or synthetic fibres. Sewport explains that plain or twill weaving may be followed by napping, which creates a raised surface and can obscure the underlying weave. That finish helps explain the familiar cosy feel.

Flannel Describes the Cloth While Plaid Describes the Pattern

Plaid, by comparison, names a pattern that can appear on many materials. A solid-coloured flannel remains flannel, while a checked fabric may have a completely different construction. Identify the surface and fibre composition separately from the printed or woven colour arrangement.