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 Flannel was originally made from carded wool or worsted yarn, but is now often made from either wool, cotton, or synthetic fiber. Flannel is commonly used to make tartan clothing, blankets, bed sheets, and sleepwear.

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 on one or both sides. If the flannel is not napped, it gains its softness through the loosely spun yarn in its woven form.

The term "flannel shirt" is often mistakenly used to refer to any shirt with a plaid or tartan pattern. However, 'flannel' refers simply to the fabric, and not all flannel shirts are plaid.