There are four common ways to put elastic in a waist. A casing threads the elastic through a fabric tunnel and is the most forgiving: it works on any fabric, and the elastic can be replaced or tightened later. Sewn-on elastic is stitched directly to the fabric and folded in, which gives a flatter waist that does not roll, and is the standard for knits and activewear. Exposed elastic sits on the outside as the waistband itself, so it saves fabric and bulk but needs a soft, good-looking elastic. Shirring gathers the waist with rows of elastic thread and gives a soft, very stretchy band for light fabrics. For a first garment or a woven skirt, use a casing; for leggings, joggers and knit skirts, sewn-on; for sportswear, exposed; for a summer top or dress in lawn or voile, shirring.
| Feature | Casing | Sewn-on elastic | Exposed elastic | Shirred |
|---|---|---|---|---|
| Fabric | Any woven or knit | Knits, light wovens | Knits, light wovens | Light wovens, light knits |
| Elastic | Any, 2 to 4 cm (3/4 to 1 1/2 in) knitted or braided | Knitted or plush, 2.5 to 4 cm | Plush-back or decorative, 3 to 5 cm | Elastic thread in the bobbin |
| Bulk at the waist | Two layers plus elastic | Two layers plus elastic, flatter | One layer plus elastic, flattest | Several rows, soft |
| Rolls or twists | Twists unless stitched through | Does not twist | Does not twist | Does not twist |
| Replace or tighten later | Easy, open the gap | Unpick the waist | Unpick the waist | Not possible |
| Stretch for pulling on | Elastic only | Elastic only | Elastic only | Very high |
| Sewing difficulty | Easiest | Needs stretching while sewing | Needs stretching while sewing | Easy, but many rows |
| Look | Soft gathers | Smooth, like ready-to-wear knits | Sporty, elastic visible | Decorative, rows of gathers |
How does each elastic waistband method work?
A casing is a tunnel. The top edge of the garment is folded down by the width of the elastic plus 5 mm (1/4 in), stitched close to the finished edge with a gap left open, and the elastic is threaded through with a safety pin, overlapped, joined and the gap closed. The fabric gathers up onto the elastic.
Sewn-on elastic, sometimes called stitched-down or fold-over elastic, is first joined into a loop the right length, divided into quarters and pinned to the top edge of the garment at the quarter marks. It is then zigzagged to the raw edge, stretched to fit between the pins, folded to the inside once, and stitched again through all layers with a zigzag, a twin needle or a coverstitch. Nothing can twist because the elastic is caught by stitching along its whole length.
Exposed elastic is sewn once to the top edge with the right side of the elastic facing the wrong side of the fabric, then flipped up so that the elastic stands above the fabric and the seam allowance sits behind it. One row of stitching along the lower edge of the elastic holds it. The elastic is the waistband, so it needs a finished top edge and a face you are happy to see: plush-back waistband elastic, a wide soft knitted elastic, or a printed decorative one.
Shirring uses elastic thread wound by hand onto the bobbin, with normal thread on top. Parallel rows of straight stitching 1 cm (3/8 in) apart, each row gathering the fabric a little more, build up a band of 6 to 12 rows. A burst of steam from the iron tightens the elastic thread afterward. There is no separate elastic to measure; the stretch comes from the rows.
When should you use a casing?
For a first garment, for any woven fabric, and for anything you might want to adjust. A gathered skirt in cotton, pull-on trousers in linen or twill, pyjama shorts, and a child's skirt that will be let out as they grow are all casing projects. The elastic can be measured generously and shortened once the garment is tried on, and years later a tired elastic comes out through the same gap.
The weakness is twisting. Elastic in a tunnel is free to roll over on itself, and a 4 cm wide elastic in a loose cotton waist will twist within a few wears. The fix is one or two rows of stitching through the casing and the elastic, in the ditch of the side seams or all the way around with the elastic stretched flat, which pins it in place. A casing also makes the bulkiest waist of the four, since it is two layers of fabric gathered up on the elastic, so it suits light and medium fabrics better than heavy ones. How to sew an elastic waistband casing covers the fold, the gap and the join.
When is sewn-on elastic better?
For knits, and for any waist that should look smooth from the outside. Leggings, joggers, a knit pencil skirt and sweatpants made from French terry use this method because it keeps the waist flat, with a single fold of fabric lying over the elastic and the gathers spread evenly by stretching as you sew.
Two things make it harder than a casing. You have to stretch the elastic evenly between the quarter marks while the machine sews it, which takes a few tries; and the elastic length is fixed once sewn, so measure first with the elastic around your body, snug but not tight. Use a knitted or plush elastic that recovers well; a cheap braided elastic narrows when stretched and loses its length. Sewing knit fabrics on a regular sewing machine has the stitch settings that let a regular machine do this.
When does an exposed elastic waistband make sense?
When bulk and weight matter more than a fabric-covered waist. Running shorts, leggings, swim-style bottoms, a sports bra band and children's play clothes all use exposed elastic, and so do lightweight wovens where a casing would gather too thickly. It uses the least fabric, the top of the garment is the elastic's own clean edge, and the one row of stitching is quick.
The elastic has to be chosen for its face. Plush-back waistband elastic, 3 to 5 cm (1 1/4 to 2 in) wide, is soft against the skin and firm enough to hold trousers up; fold-over elastic gives a narrower, bound edge for underwear and children's clothes. A plain white braided elastic looks unfinished on the outside, and that is the most common reason an exposed waistband disappoints. As with sewn-on elastic, the length is fixed once stitched, so measure it on the body first.
When should you shirr the waist instead?
For light, soft fabrics and a soft, forgiving fit: a summer dress with a shirred waist in cotton lawn, voile or crepe, a child's sundress, a peasant top. Shirring stretches far more than a single elastic, since every row contributes, and it fits a range of waists without any measuring. It is also decorative: the rows of gathers are the design.
The limits are fabric weight and durability. Elastic thread cannot pull up a medium or heavy fabric, so shirring is for fabrics up to about 120 gsm (3.5 oz per square yard). It is also the least repairable method: when the elastic thread tires, the rows have to be unpicked and resewn.
How long should the elastic be?
For a casing, sewn-on or exposed waist on wovens and stable knits, cut the elastic to the waist measurement minus 2 to 5 cm (3/4 to 2 in), plus 2 cm (3/4 in) for the overlap. Firm knitted elastic and stretchier fabrics take the larger reduction; soft elastic and wovens the smaller. Always try the loop on before you sew it to the garment: it should hold the garment up without leaving a mark after an hour. The elastic length calculator gives a starting figure by elastic type and waist, and Sewly's sewing guide lists the elastic length for your own waist in the notions of any pull-on garment.
Which should you choose?
- A first skirt, pyjama shorts or trousers in a woven: a casing, with a row of stitching through the side seams to stop twisting.
- Anything you might need to let out or tighten later: a casing.
- Leggings, joggers, knit skirts, sweatpants: sewn-on elastic, finished with a twin needle or coverstitch.
- Running shorts, sportswear, underwear, swim-style bottoms: exposed plush-back or fold-over elastic.
- A summer dress or top in lawn, voile or crepe: shirring, six to twelve rows.
- Children's clothes that must last several sizes: a casing, with extra elastic length left inside.