This tutorial will teach you two ways to sew an elastic casing – by folding the edge in twice, or using bias binding/tape. Either of these methods works well for waistbands, cuffs, leg openings, etc. Both ways has the elastic threaded into the casing, rather than being stitched directly to the fabric. This allows for easy elastic adjustments, or even replacing the elastic if ever needed.
How to make a double fold/hemmed elastic casing
Determine the width of the folds
If you’re not following a pattern that tells you how much to fold your fabric, just make the folds 1/8 inch wider than the elastic. This extra 1/8 inch is for the edge stitch and for some extra space for the elastic. If you think you can’t get your edge stitch very close, then add a little more width than this.
Iron the folds and pin
Fold the fabric to the wrong side and iron, then repeat, and pin in place. On this diaper cover, I used 1/2 inch elastic in the waist, with 5/8 inch folds. And I used 1/4 inch elastic in the legs, with 3/8 inch folds. The legs are a bit more tricky to fold and sew, because they have concave curves. I’m working on a tutorial for how to do that easily, which I’ll link to here once it’s done.
Edge stitch, leaving an opening to thread elastic through
Edge stitch about 1/16 inch from the edge. You will have the fabric facing wrong side up. Start and end about 1/2 inch from the center back (or wherever makes sense for your project). This will leave a 1 inch opening to thread the elastic through.
And your casing is complete! The instructions for threading the elastic through are further below, after the bias binding casing.
How to make a bias binding casing
Some people prefer to always use bias binding for curved elastic casings. Personally, I only use it when folding twice won’t work. Although it’s an extra step, it can also be a little easier because the binding curves so easily. You’ll just have to see what you prefer!
If you don’t know how to sew bias binding, you can check out my post on How To Sew Bias Binding On Clothing here. The post also includes a handy conversion chart for all the different bias binding/tape sizes in imperial and metric, as well as store bought vs homemade bias binding.
Determine the size of bias binding
Just like with the folds above, you will want the size of the bias binding to be slightly wider than your elastic, to allow extra space for stitching and for the elastic to move.
I used 1/4 inch elastic, and homemade 1/2 inch single fold bias binding for this romper bottom.
Sew the binding onto the main fabric
In this example, I’m just sewing from the front to back of each leg, and then the raw edges will be covered with a snap placket. But if you were sewing in a circle, like a closed leg, just make the ends overlap diagonally. (More info on how to do this in my article How To Finish Bias Binding Ends, if you don’t know how).
So, sew the bias binding onto the main fabric, right sides together, stitching in the fold.
Iron seam allowance towards bias binding
Although understitching is common with bias binding, it does add some stiffness. So I don’t do it for elastic casing. Iron the seam allowance toward the binding instead. This will help with folding in the next step.
Edge stitch bias binding in place, leaving an opening to thread elastic through
Fold bias binding to wrong side. Make sure the binding is folded over enough so that it can’t be seen from the right side. Edge stitch. If you’re sewing in a closed circle, make sure to leave an opening to thread the elastic through!
How to insert elastic into casing
Determine the elastic length
If you’re not following a pattern that tells you how long to make the elastic, then measure the circumference of whatever body part this is going on (leg, waist, etc.). You will want to add an extra 1/2 inch for the overlap, and probably some extra length for comfort.
Thread the elastic through the casing
Place a safety pin on one end to thread the elastic into the opening and all around. I like to actually use a safety pin on each end. This is so that the end that I’m not working with can freely pull into the casing as needed, and then I can pull it back out when I’m done. This helps to reduce the chance of the elastic twisting, as well as permanently folding (which happens when the first end gets stretched too much).
Pin ends, overlap, and sew
Once you have the elastic threaded all the way around and pulled back through the opening, you can overlap the ends by 1/2 inch and pin. Once it’s pinned, double check that there are no twists. Then pull it out enough to give yourself some space to sew.
Place under the presser foot in the following way, with the pin still in the elastic. You can use a regular straight stitch, because you will be stitching across the elastic, which is not the stretchy part. Turn the handwheel towards you to make one stitch to secure the ends, then remove the pin.
Then stitch forward and back a couple times. This part can be a bit tricky, as the elastic might want to shift or get stuck. Just take your time and help it along if needed. Then shift the elastic over, and sew another line that’s parallel to the first.
Then stretch out the section and the elastic will pull into the casing.
Sew opening closed
And finally you can sew the opening closed, making sure to backstitch. As you can see, I also added a little folded piece of twill tape on this diaper cover, to indicate the back.
Elastic threaded into an elastic casing with open ends
If you’re threading elastic through a flat section with open ends, like this romper bottom with a snap placket, then you can simply thread the elastic through in the same way. Once you have it all the way through, pin both ends. Then sew to secure. In the picture below, I’m sewing both front ends, just going straight across. I made sure to backstitch over the elastic, to really secure it.
And that’s how to easily sew an elastic casing and insert the elastic!
I hope you found this tutorial helpful. Be sure to let me know if you have any questions in the comments below!
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