A casing is a tunnel of fabric holding a cord or elastic. The two things that go wrong are the channel being too tight and the openings being made too late.
Make the openings first. Whether the cord comes out through two buttonholes on the right side, or through a gap left in a seam, that has to be done while the fabric is flat and accessible. Reaching into a finished casing to make a buttonhole is unpleasant and usually untidy.
Reinforce behind the openings with a small patch of interfacing. That is where all the strain lands, and an unreinforced buttonhole in a casing tears out.
Size the channel generously. Measure the cord flat and add at least 6 mm, more for a thick cord. A cord that binds in its channel cannot be drawn evenly and the garment gathers unevenly.
Fold and press. Turn the raw edge under, then fold to form the channel and press. Stitch close to both folded edges — the lower edge closes the channel and the upper edge stops it rolling.
Thread the cord with a bodkin or a safety pin, working the fabric back along the cord rather than dragging the pin through.
Secure the cord ends — knot them, finish them with metal ends, or stitch a stop so the cord cannot be pulled out of the channel entirely.
A separate applied casing, made from a strip of fabric or bias binding stitched on both edges, is the better answer where the garment edge is curved or where the casing does not sit at an edge.
Questions people actually ask
How wide should the casing be?
The width of the flattened cord or elastic plus at least 6 mm, so it can be drawn through freely.
My drawstring twists inside the casing.
Almost unavoidable with a round cord. Stitch through the cord at the centre back to anchor it, or use flat tape instead.
Last reviewed 2026-08-11