Bias cut trews are based on early trousers, which replaced knee-britches worn with knitted hose as practical leg coverings for men. They are cut entirely on the bias (diagonal) of the fabric, so they will stretch around the knee and seat, shaping to fit the wearer over time. Each leg is cut in a single piece, with no outside seam, just a dart running down from the waist to the hip, to allow for some shape and to hold the side pocket opening.