What a casing is and why it matters
A casing is a tunnel of fabric that runs around the waistline — the elastic slides inside it, hidden from view. Instead of sewing the elastic directly to the fabric, you fold the fabric edge inward, stitch it down to create a channel, and then thread the elastic through. This method gives you a finished, professional look and makes it straightforward to replace the elastic later without unpicking seams.
The casing approach works best on garments where you want a clean inside finish: pajama pants, drawstring shorts, skirts, and athletic wear. It takes a bit longer than direct attachment, but the result lasts longer because the elastic isn't under constant stress from being sewn to fabric.
Key Takeaways
- Fold the fabric edge down by the width of your elastic plus half an inch, press it flat, and stitch close to the fold to create the casing tunnel.
- Use a safety pin or bodkin to thread the elastic through the casing without bunching or twisting it.
- Overlap the elastic ends by half an inch and stitch them together with a zigzag or box stitch before closing the casing opening.
- Try on the garment before sewing the casing shut to make sure the elastic sits at the right height and feels comfortable.
- Measure your elastic against your body, not the garment — it should pull snug but not cut off circulation.
Measuring and cutting your elastic
Measure the elastic around your actual waist or hips (depending on where the garment will sit), then subtract one to two inches so it pulls the fabric in slightly without pinching. For example, if your waist is 30 inches, cut elastic that is 28 to 29 inches long. Write this number down — you will need it later.
The width of your elastic depends on the look you want. Quarter-inch elastic creates a thin, delicate line; half-inch is standard for most pants and skirts; one-inch elastic gives a wider, more supportive band. Check your pattern for a recommendation, or look at similar finished garments to see what width feels right.
Preparing the fabric edge for the casing
Trim the seam allowance at the waistline down to a quarter inch if your pattern gives you a standard half-inch allowance. This reduces bulk inside the casing. Press the trimmed edge flat with your iron.
Fold the fabric edge down by an amount equal to your elastic width plus half an inch. If you are using half-inch elastic, fold down one inch total. Press this fold firmly with your iron so it holds its shape — a sharp crease makes stitching much easier and keeps the casing even all the way around.
Pin the folded edge in place every two to three inches. Check that the fold is the same distance from the edge all the way around the waistline. If the garment is gathered or has a lot of fullness, distribute the gathers evenly under the fold before pinning.
Stitching the casing
Stitch close to the bottom fold of the casing — this is the edge closest to the body of the garment. Use a straight stitch and sew all the way around, removing pins as you go. Backstitch at the beginning and end. This line of stitching creates the bottom wall of your elastic tunnel.
Now stitch a second line near the top of the folded fabric, about a quarter inch below the raw edge. This creates the top wall of the tunnel. The space between these two lines is where the elastic will live. Backstitch at the beginning and end of this line too.
Leave a two-inch opening in one of these seams — usually the back seam or a side seam — so you can thread the elastic through. Do not stitch across this opening; you will close it by hand after the elastic is in place.
Threading the elastic through the casing
Attach a safety pin or bodkin to one end of the elastic. A safety pin works in a pinch; a bodkin (a flat, pointed tool made for this job) is easier to push through without snagging. Insert the pinned end into the opening you left in the casing.
Push the safety pin through the tunnel slowly, bunching the fabric onto the pin as you go. The elastic will follow behind. Work your way all the way around until the pinned end comes back out the same opening. Remove the safety pin.
Overlap the two elastic ends by half an inch inside the casing. Pin them together so they do not slip. Try on the garment and check that the elastic sits where you want it and feels comfortable — not too tight, not too loose. Adjust if needed before sewing.
Joining the elastic ends
Stitch the overlapped elastic ends together with a zigzag stitch or a box stitch (a square with an X through it). Zigzag is faster; box stitch is stronger. Either way, make several passes to may support the seam will not come apart with wear. The stitches should go through both layers of elastic.
Trim any excess elastic that sticks out past the seam. Push the joined elastic back into the casing so the seam sits inside the tunnel and does not create a lump.
Closing the casing opening
Fold the raw edges of the opening inward by a quarter inch on each side and press them flat. Pin the opening closed. Using a needle and thread that matches your fabric, sew the opening shut with a ladder stitch (also called an invisible stitch). This stitch runs inside the fold of fabric and is nearly invisible from the outside.
If a ladder stitch feels too fiddly, a straightforward whip stitch around the perimeter of the opening works fine — it will be visible but neat. Backstitch at the beginning and end to lock the thread.
Frequently Asked Questions
What if the elastic twists while I am threading it through?
Stop, reach in with your fingers, and untwist it before continuing. Twisted elastic will create lumps and sit unevenly. It is worth taking a few extra seconds to keep it flat as you push it through.
Can I use a drawstring instead of elastic?
Yes. Use the same casing method but make the tunnel slightly wider — about half an inch larger than your drawstring width. Thread the drawstring through with a safety pin, and tie the ends in a knot or bow at the front or back.
What happens if I sew the casing too tight?
The elastic will not slide through easily, and you risk puckering the fabric. If this happens, carefully cut a small slit in the casing seam, thread the elastic through, and hand-stitch the slit closed. Next time, leave a slightly larger opening or use a wider casing.
Do I have to leave an opening, or can I stitch the casing completely closed?
You need an opening to thread the elastic through. If you stitch it completely closed, you will have to unpick stitches later to insert the elastic — it defeats the purpose of the method.
How do I replace the elastic if it wears out?
Open the casing seam at one spot by carefully cutting a few stitches. Thread out the old elastic and thread in the new one using a safety pin. Stitch the opening closed. This is one of the main advantages of a casing — you can refresh the elastic without rebuilding the whole waistband.