Last week I explained how the zig zag stitch is stretchy, but that’s only half the story! You also need it to be the correct size and tension for your project.

The goal of a properly formed and tensioned zigzag stitch for sewing knits is to have no resistance when you stretch the fabric. This is important because as you pull the fabric over your head, or you hug a friend, or you reach for that jar of tomatoes, you won’t break the stitches of your garment and risk having it start to fall apart.

For the video, each zig zag is the same width and length (3x3 - refer back to this post if you need a refresher). So why do they act so different in the fabric? First let’s see what they do.

In the first video below you’ll see that the top zigzag stitch is visibly distorting the fabric even when under no tension (ie: I’m not touching anything yet). When the fabric is pulled, the stitches resist the stretch and don’t move with the fabric. This is NOT what you want. The stitches will either break over time or worse, shred your fabric seamline due to tension.

In this second video, the bottom zigzag doesn’t distort the fabric. When the fabric is pulled, the stitches flatten from “v” shapes to a straighter line and then return to “v” shapes when the fabric is released. This allows the garment to stretch WITH you as you move and doesn’t break your stitches.

Here’s the differences as I sewed them. The top line of stitching used a too large needle and “auto-tension” on my machine. The second line of stitching uses the correct size and type of needle for the fabric and I’ve loosened the tension until I have equal tension on both the needle thread and the bobbin thread. This allows the thread to move with the fabric as the fabric stretches!

You should always test your stitch on a knit scrap before sewing your garment. Here’s how:

• Make sure you have about six inches or so of folded material. You’ll want to sew on two layers and sew on the cross-grain (or whichever has more stretch).

• Make sure your needle size and type match your fabric!

• Test about four inches of stitches and take your fabric out of the machine.

• Use your thumb and index fingers to firmly pinch each end of the seam. Now stretch the fabric. If you can feel resistance, then you’ll need to adjust your stitch before constructing your garment. If you feel no resistance, like all you’re doing is stretching fabric, and your stitches are not hanging loose, then you’re ready to sew!

• If you feel resistance try making your stitch narrower if you are able. Sometimes it takes a bit of fiddling to get the stitch just right for your fabric.

• Keep in mind that the stretch of your fabric can affect which size zigzag you choose! Always test before sewing, because ripping out zigzag sucks.