It can be pretty annoying when you finish hemming that cute body con dressonly to see that the bottom edge looks wavy, curvy, puckered --whatever you want to call it, just notflat. So, I come to your rescue (hopefully☺️) with my top 3 tips on how to hem stretchy fabrics so that they lay flat. Alright, on with the tips:
The straight stitch is not a friend of knit fabric, stick with a zigzag stitch, and yes, it's stretchy fabric but you do not need to stretch it (nor put pressure on it ) while you're sewing it. A zigzag stitch is better with stretch fabric because the unlike the straight stitch, the gaps between the zigzag stitches allow your fabric to stretch without breaking the stitches.
For stitch length I recommend 2.5 or anything in the middle, the width in the middle maybe 2.5 as well. For the tension in the middle 4.5. You do not want to put pressure on your fabric while you're sewing because that will cause it to stretch just keep your finger lightly on the fabric and use your finger as a guide for the fabric so that it goes through straightly and evenly.
My second tip is Wash Away Wonder Tape, this thing is amazing! To put this baby in action, first decide how much tape you need for your garment. On one side of the tape there is a sticky transparent film, and on the other side there is white facing, which you will be separating from the adhesive film. With the wrong side of your fabric facing up, place the sticky side of the tape onto the fabric, and smooth it down (you can also use an iron if you'd like). It's better to rip off the end of the tape because that way you will naturally start to see the clear part separating itself from the white layer. Hold on to the clear part and peel off the white side.
Once you've applied the Wonder Tape, fold over your fabric the way you would if you were to hem it. The beauty of this tape is that you don't need pins to keep the fabric in place before sewing. Heck, if you wanted to, you could opt not to sew after you've applied your Wonder Tape (but that's honestly not a route I would take). To keep the tape in place iron down the hem before you zigzag stitch over it.
This is what my hem looks like after using the Wonder Tape.
My number one tip for hemming stretchy fabric is the twin needle. The twin needle comes in different sizes, and each size determines how far apart each row of stitches will be. My pack of needles came with a pin tuck foot, but you can use a zigzag stitch foot or a regular straight stitch foot instead.
To thread the second needle you'll need another spool of thread, or you can simply use a bobbin. Thread your machine the same exact way following the same steps but this time don't put the thread behind the metal loop. Instead, just skip the loop and directly pass the thread through the second needle. 1. If you place both threads (the main thread, and the one from the bobbin/second spool) behind the metal loop, you'll cause the threads to tangle. 2. It doesn't matter which needle you thread first, personally I start with the needle on the left.
Make sure that you're using straight stitch in order to prevent your needles from breaking. Again, do not stretch the fabric while sewing, just use your fingers to guide the fabric. Keep in mind that the side of the fabric that is facing up while you're sewing will have the double rows of stitches, and the other side will have zigzag stitches. So, if you want the zigzag stitches to be on the wrong side of the fabric, you'll have to sew with wrong side facing up.
My bonus tip for hemming stretchy fabric is ...the iron!! if you iron your hem as your final step you'll get a flat lay and a professional finish.