Twilled fabrics are a type of woven fabric that have a distinct pattern of diagonal parallel ribs. The two most common types of twilled fabrics are serges and reps. Serges are a type of twill fabric with a smooth, even surface and a diagonal rib on the face and a plain back. Reps are a type of twill fabric with a more pronounced rib on the face and a plain back. Both serges and reps are commonly used in apparel, upholstery, and other textile applications.