flank

A flank is a side pocket set into the back panel of trousers, typically positioned at the intersection where the seat meets the side seam. Unlike patch pockets sewn on top of fabric, flanks are cut and stitched as integral parts of the garment structure, with the pocket mouth opening along the existing side seam or a reinforced line parallel to it. The pocket bag itself is usually constructed from a lighter cotton or lining fabric to reduce bulk and weight.

Flanks appear as a pair, one on each side of the seat, and serve both functional and aesthetic purposes. They allow the wearer to carry items like keys or a wallet without the visibility or weight distortion of front pocket contents. From a manufacturing standpoint, flanks require precise pattern marking and seaming because the pocket opening must align exactly with the trouser's finished side seam, and the bag must be sewn in before the side seam is closed.

Construction and Common Issues

The most frequent manufacturing defect is pocket gaping, which occurs when the pocket mouth puckers or pulls away from the seam during wear. This happens if the pocket bag is cut too small, if the side seam allowance is inconsistent, or if the reinforcement stitching that anchors the pocket opening is not strong enough. The pocket mouth should be understitched or topstitched to keep the bag from rolling outward.

Flank construction adds labour cost compared to patch pockets because it requires additional pattern pieces, careful positioning, and precise seaming sequences. The pocket bag itself can fail under stress if made from fabric too thin or if the seam that attaches it to the trouser panel lacks sufficient stitch density. Industrial production typically reinforces the top corners of the pocket bag with small triangle stitching to prevent corner tears.

The term flank comes from the side or outer position of the pocket relative to the trouser's profile. In ready-made menswear and workwear, flanks are standard; in tailored or formal wear, they are less common because a side pocket opening can interrupt the clean line of a jacket or waistcoat silhouette. The construction method has remained largely unchanged since the early 20th century, making it a durable and recognizable feature of mainstream trousers.