Definition
A casing is a fabric tunnel along an edge, made by folding the fabric over or adding a band, that holds elastic or a drawstring.
Casings are the simplest way to gather a waist, cuff or neckline without a zip. The most common is the fold-over casing: the edge is turned under twice and stitched, leaving a channel wide enough for the elastic. A separate band of fabric can also be sewn on as a casing, which is neater on shaped edges.
Make the channel slightly wider than the elastic: about 3 to 6 mm (1/8 to 1/4 in) of extra width lets it slide through and lie flat without twisting. For a 2.5 cm (1 in) elastic, a channel about 3 cm (1 1/4 in) wide works well.
The usual method:
- Fold and stitch the casing, leaving a gap of about 5 cm (2 in).
- Thread the elastic through with a safety pin or bodkin, holding the far end so it does not disappear inside.
- Overlap the ends by 2 to 3 cm (3/4 to 1 1/4 in) and zigzag them together, then close the gap.
Stitching through all layers at the side seams afterward keeps the elastic from rolling. Sewly's pull-on trousers and shorts use an elastic casing, and their sewing guide gives the elastic length. Full steps are in how to sew an elastic waistband casing; to size elastic yourself, use the elastic length calculator.