I cut strips of lycra across the width of fabric, using a rotary cutter and quilting ruler. I find that using a rotary cutter and ruler give me a more even cutting width than by using scissors. For all of the straps below, I have used powdered, rubber elastic, width 6 mm (sourced here).
(5 methods will be shown)
Method 1: Wrap around, sewing machine
For this method, cut the strip of fabric 3 x elastic width, taking into account the thickness of the elastic. My elastic is 6 mm wide and 1 mm thick, so I have used 3 x (1+6) = 21 mm strap width.
Sew the elastic to one edge of the fabric using a 3-step zig-zag stitch. If you don't know what a 3-step zig-zag is, click on the photo below. You can also see that I have used a stitch width of 4 and a length just below 2.
I have used a ribbon foot to guide the elastic. You do not need this, it just helps me keep the elastic straight. You may have another foot with a guide to keep both the elastic and fabric straight.
This is what is looks like after the elastic is attached.
Wrap the fabric around the elastic and stitch again, using a plain zig-zag stitch. I have used a width and length of about 3.
Here you can see both sides of the finished strap. The strap is flat. You could use a twin needle or a cover stitch machine for the second pass of stitching if you prefer.
Method 2: Wrap around, overlocker + sewing machine
This method is essentially the same as above, except that the first pass is done on an overlocker.
When attaching elastic to lycra, I usually lengthen the stitch on my overlocker to its longest setting.
On the advice of my sewing machine mechanic, I thread the needle thread through the left most tension dial, for 3-thread overlocking, even if I am using the right needle position.
For this method, I cut the fabric wider than I need, and trim it later. I do this because I tend to have less control with the overlocker than the sewing machine, and am not as consistent with my sewing position. I have cut a fabric with of 30 mm for 6 mm wide elastic.
First I use the overlocker to attach the elastic to one side of the fabric. Because I have used a wider fabric than I need, it doesn't matter if the overlocker trims the fabric a little. You do not want the overlocker to cut the elastic.
You can see that I stretched the elastic a little as I applied it.
I then wrap the fabric around the elastic and stitch it down using a zig-zag stitch (length 3, width 3) on a regular sewing machine. You could use a twin needle or a cover stitch machine for this second pass of stitching if you prefer.
Here is a photo of the stitched strap.
It is fairly easy to trim the excess fabric away neatly.
Completed strap. Again, quite a flat strap.
Method 3: Tubular strap, sewing machine
For this method, the fabric is cut at least 5 mm wider than 2 x elastic width. I have used a fabric width of 25 mm for 6 mm elastic.
Fold the fabric strip in half, right sides together. Align the elastic a little to the right of the fold. If you align it right on the fold, the tube will not be wide enough. The distance away from the fold should be equal to the width of stitching into the elastic, but a couple of millimetres will do if you are not sure.
Use a zig-zag stitch to stitch down the right edge of the elastic. You want to catch the elastic in the left swing of the zig-zag but go off the edge of the elastic in the right swing of the zig-zag. I used a width of 3 and a length of 3, but I recommend closer stitching, as you will see later.
Make a snip in the folded edge of the elastic, about 1 cm from the end of the tube.
Slide a bobby pin over this end of the tube and then into the tube to turn through.
Completed tube. This part looks okay but...
Some of the stitches popped when I was turning the tube.
You can tie a knot to neaten the end of the strap.
I repeated this method, using a zig-zag stitch length of 2.
This results in a beautiful strap with no popped stitches. The seam line sits in from the edge of the strap, so the strap does not sit perfectly flat. If you look at the straps of commercially produced swimwear, you will see this same effect, so don't worry about it. These types of straps are often used as ties on bikinis.
Method 4: Tubular strap, overlocker
This method is similar to method 3 above, only using an overlocker.
I found I did not have as much control as using a sewing machine.
The fabric and lycra slipped around, making it hard to keep a consistent distance from the folded edge.
The final result looked okay though. Of course it would look better with matching thread.
Method 5: Plaited strap.
Some days you just can't get the results you want. Your machine may not be feeling friendly. Some elastics don't behave nicely. Perhaps you have broken your last stretch needle? Well, don't despair. You can make pretty straps without a sewing machine.
Cut 3 strips of fabric, each 1 cm wide. They don't have to be contrasting colours. You can use a printed fabric.
Knot the strips together. Secure the knot in position. I usually open a desk or kitchen drawer, put the knot inside and close the drawer again to secure. Plait away. The strips tend to curl, so if you are using a printed fabric, try to get the fabric to curl inwards so that all the colour shows in the plait.
Finished strap. I started with 50 cm lengths. The final strap was just longer than 50 cm, so the fabric must have stretched whilst I was plaiting it. The final strap still has good stretch and recovery, though perhaps not quite as good as the elastic straps above.
My favourite methods are 2&3 as these give me the neatest results for the least hassle. I would choose between 2 and 3 depending on the use for the strap.