What Is a Casing in Sewing? Channel Construction Guide

Self-fabric casings are created by folding the garment edge over to the inside and stitching it in place, forming a tunnel. This method is the most common for elastic waistbands and drawstring closures. The width of the fold must be sufficient to accommodate the elastic or cord with enough ease for it to move freely. A casing that is too tight will restrict the stretch of the elastic, reducing comfort. A casing that is too wide will allow the elastic to twist or roll inside the channel.

Applied casings use a separate strip of fabric stitched to the garment to form the channel. This approach is used when folding the garment edge is not practical, such as at a waistline that does not fall at a hemmed edge, or when the designer wants the casing on the exterior as a design detail. Bias tape casings are a subset of applied casings that use pre-folded bias tape, offering a neat, lightweight channel suitable for lightweight fabrics and curved applications.

The elastic waistband is the most widespread application of casing construction. The top edge of a skirt, pant, or short is folded to the inside, pressed, and stitched to form a channel. Elastic is then threaded through the channel, secured at both ends, and the opening is closed. The width of the casing should be the width of the elastic plus one-quarter to three-eighths inch of ease. This ease allows the elastic to stretch and recover without binding against the fabric.

For production efficiency, the casing often includes a small opening left in the stitching, through which the elastic is inserted with a bodkin or elastic threader. After the elastic is inserted and joined, the opening is closed with a short line of stitching. In higher-end garments, the casing may be fully closed during sewing and the elastic attached to the seam allowance with a stretch stitch, eliminating the need for a separate opening and giving the waistband a cleaner finish.

Drawstring casings function similarly to elastic casings but include an exit point where the cord emerges from the garment. This exit can be a buttonhole cut into the casing before stitching, a metal eyelet or grommet punched through the fabric, or an opening at a seam junction. The placement of the drawstring exit affects both the function and the aesthetic of the garment. Centered exits create symmetric gathering when the cord is pulled, while side-positioned exits allow the cord to serve as a visual detail.

The cord or drawstring itself must be specified in the tech pack, including material, diameter, length, and any end treatments such as aglets, knots, or cord stops. The casing must be wide enough for the cord to slide freely. In production, drawstrings are typically inserted after the casing is sewn, using a bodkin or safety pin to guide the cord through the channel. For very long drawstring runs, such as a full-circumference hood casing, a cord threader tool makes the process faster and more reliable.

In structured garments like corsets, strapless bodices, and boned skirts, casings hold strips of boning that provide vertical support and prevent the fabric from collapsing. Boning casings are narrow channels stitched to the inside of the garment, usually aligned with seam allowances or attached to the lining. The channel must be the exact width of the boning plus minimal ease to keep the bone from shifting while allowing it to be inserted and removed for laundering or replacement.

Common boning materials include steel spiral boning, which is flexible in all directions and used for form-fitting corsets, and plastic boning such as Rigilene, which is lighter and less expensive. The casing fabric for boning is often a tightly woven cotton or poly-cotton twill that resists puncture from the boning ends. Boning channels are typically closed at the bottom with a bar tack or small stitched pocket to prevent the bone from poking through.

A thorough tech pack casing specification includes the casing type, width, the enclosed element and its dimensions, and the method of insertion and securing. For elastic casings, note the elastic width, stretch percentage, relaxed and stretched lengths, and whether the elastic is sewn through or free-floating. For drawstring casings, specify the cord material, diameter, total length, exit type, and any hardware.

Include a cross-section diagram showing the casing construction layers: garment fabric, fold or applied strip, stitching lines, and the enclosed element. This visual reference is invaluable for factory operators who may be unfamiliar with the specific casing design. Skema3D and other digital garment tools can simulate casing details on 3D models, showing how the gathered or cinched effect will look on the finished garment. This visualization helps designers refine casing width and elastic tension before the sample stage.