Flannel is a soft woven fabric, of various fineness. Flannel was originally made from carded wool or worsted yarn, but is now often made from either wool, cotton, or synthetic fiber. Vegetable flannel is made from Scots pine fibre.

Flannel may be brushed to create extra softness or remain unbrushed. Brushing is a mechanical process wherein a fine metal brush rubs the fabric to raise fine fibres from the loosely spun yarns to form a nap. Typically, flannel has a nap on either one side or both sides. If the flannel is not napped, it gains its softness through the loosely spun yarn in its woven form.

Flannel is commonly used to make tartan clothing, blankets, bed sheets, and sleepwear. The term "flannel shirt" is often used incorrectly to mean any shirt with a plaid or tartan pattern.