What is flannel?
Flannel is a warm fabric of various degrees of weight and fineness. It is a plain-weave cloth heavily brushed for softness. Flannel is often used in apparel and sheets, and can be made of cotton or wool. The brushing process creates insulating air cells that provide more warmth than plain cotton. From the Welsh word gwlanen, or "wool," flannel has become a fabric staple for cotton pajamas and robes, men's shirts, bedding and has become a favorite of quilters all over the world. (random internet search, articulated well ;)