On Zippers in Knits
I made a Cowichan-inspired jacket many years ago, and it was perfect. I absolutely loved it. Until I sewed the zipper in. Then it was a disaster: I had chosen the wrong length and type of zipper, and then I did a rush job of sewing, by machine.
So I cast any thoughts of zippers out of my mind. For twenty years.
I was in New York City last fall. The weather was cool and crisp, the right time of year for jackets. And every stylish woman I saw was wearing a leather motorcycle jacket. And no matter how they were styled or the age of the wearer, each one looked fantastic. By the time my friend arrived for lunch, wearing hers, I knew I had to have one, too.
But I’m a knitter, so I decided to design and knit it. I was about halfway through the knitting when I realized that the zipper details I was planning would require … well, zippers. Like, three of them. And I’d have to sew them in.
The first measly six-inch sleeve zipper took me about four hours. But by the time I was done, I realized everything I’d done wrong the first time around.
And so, to save you a sweater disaster and many hours of unpleasant learning, Kate’s Guide to Zippers in Knitwear.
In the MDK Shop
Lesson 1: Choose the Right Zipper
If you’re making a jacket or cardigan, make sure you get a zipper that fully separates. That is, a zipper for which you can separate the two parts. (You know, like on a coat.) These are called, handily enough, Separating Zippers.
The other type—think of the fly of your jeans—separates at one end, but not the other. This is the type I used for my jacket sleeves’ cuffs. Be careful, though: I initially bought a bag zipper by mistake, and that one is closed at both ends.
Consider not just the length, but the weight: A zipper for knits needs to be heavier than a zipper for woven fabrics. Good quality zippers will be labelled with a number that indicates the width of the coil/teeth, when closed, in tenths of cm. I used a #10 for my jacket, which has teeth that are a full 1cm (10mm wide). This is pretty extreme, but #5-8 aren’t unreasonable for knit fabrics.
The one at the top has a coil-style closure, rather than teeth. These are too light. The one at the bottom is plastic pretending to be metal. The center one is the best choice for a heavier weight knit fabric.
A zipper with traditional metal rather than plastic teeth is generally a better weight for a knit jacket; choose plastic teeth or a coil-style zippers for lighter fabrics.
Lesson 2: Consider the Fabric You’re Sewing To
The problem with sewing a zipper into a knit is that you’re sewing something stiff and stable—the zipper tape—onto something that isn’t. If the knit fabric relaxes after the zipper is installed, then you’re going to have puckers; if the knit fabric is stretched as you attach the zipper, the you’re going to have a bubbled, buckled zipper.
For best success, you want to inhibit the stretch and movement of the knit fabric where the zipper will be attached. There are a couple of ways to do this.
Use a tighter and more stable edging where the zipper will be installed. For example, on my jacket, I wanted the zipper to be exposed, so I needed the simplest possible edge on the fabric. I worked a slipped stitch edge, and kept it fairly tight.
If you want the zipper to be hidden, work a picked-up i-cord edge on your knit fabric. Ensure it’s reasonably snug, pulling the stitches tight as you go. The zipper tape will hide nicely under the i-cord.
If your garment has a ribbed or other type of band worked after the fact, consider the possibly-rather-radical-step of working it separately and sewing it on, rather than picking up the stitches. And make sure your bind off is firm—this is not a place for a Jeny’s Surprisingly Stretchy method. You’ll then have a stable edge, and can then attach the zipper either to the seamed join, or the bind off edge.
Or take a tip from those ubiquitous Scandinavian colorwork sweaters: ribbon. Hand sew a length of woven/grosgrain ribbon along the edge of the knit fabric, on the inside to provide a tidy base to sew the zipper to. Or sew it on the outside to create a decorative effect. Either way, the ribbon will stabilize the fabric and give you a good place to pin.
Learn from Kate’s Mistakes Part 1: Pay for a good quality zip. You don’t want to have to do this a second time when a cheap one breaks or gets stuck.
Lesson 3: Wash Before You Put the Zipper In
You should always block the pieces before you put a garment together. Just like pre-washing woven fabrics, you need to bring the fabric to its final, correct shape and size before you finish. To block, wash the garment pieces the way you’ll wash the finished garment.
If, after the wash, the edges of the opening are still extremely rolly, steam or lightly press them to make them behave. Caro Sheridan brilliantly recommends using blocking wires to stabilize the edge you’re sewing to – feed one along each edge of the garment, before you pin.
Learn from Kate’s Mistakes Part 2: Do it by hand. You’ll need long sewing pins, strong sewing thread in a color that contrasts both the zipper and the garment, and in a color that matches your garment, and a sharp hand-sewing needle.
Lesson 4: Pin and Baste and Sew
Lay the garment pieces flat. Open/separate the zipper, and carefully pin the tape along the edge of your garment, placing pins every inch or so, perpendicular to the direction of the zip. Close the zip and make sure it all aligns and lies tidy.
The zip is pinned along a slipped stitch edge, ready for basting.
The edge of the knit fabric is about a quarter inch away from the teeth. You want the zipper visible, not the tape. It does pull away a little once it’s sewn in.
In this case, I want the zipper to be hidden when it’s closed, so I’ve worked i-cord at the edge.
When pinning, make sure that the i-cord just covers one side of the teeth.
Using the contrasting color thread, baste it in. This is just to assess the placement, so use long stitches—half an inch (a centimeter) or so. Work from the right side of the garment, up and down in the space between the first and second stitch of the knit fabric (the same column you work in for mattress stitch).
I’m working in the column between the first, slipped, stitch and the second stitch of the row.
Take all the pins out and try the garment on to make sure it’s well placed and the fabric isn’t puckering or uneven. Ensure it looks good with the zipper open and closed.
Once you’re happy with the basting, then using the matching thread, sew the zipper in, using smaller stitches, closer together. Always work from the right side, still in the same column, so you can ensure your stitches are aligning with the knit fabric.
Try it on again.
And if that’s good, remove the basting. Then use the matching thread to whipstitch down the sides of the tape on the inside, just catching the inside bump of the knit fabric.
If you’re using ribbon, sew it on the inside, just inside the edge stitch, and then sew the zipper to the ribbon.
The ribbon not only stabilizes the edge of the knit fabric, but it gives you a wider base to pin to.
Alternately, sew the ribbon on the outside and sew the zipper so that the knit fabric is sandwiched between the zip and the ribbon.
Learn from Kate’s Mistakes Part 3: Be patient. This is not something to do in the final hour before you go to bed, in half-light in front of the TV, after a glass or wine or two. This is a quiet weekend morning activity.
Learn from the Experts: All my sewing books tell me to sew both sides of the zipper tape in the same direction. Any tension or pulling on the fabric is then in the same direction on both sides. It can help things look that little bit tidier.
Learn from Kate’s Mistakes Part 4: If you don’t like it, put your big-girl pants on, undo it and start again. If you don’t like it now, you’re not going to come around to loving it over time.
Lesson 5: Wash/steam After It’s In
To make it gorgeous and tidy and perfect, it’s worth another steam or wash. Because you’re going to wear this thing with great pride, and everyone is going to want to admire your zipper success. Trust me.
Save it for Later
Don’t need to install a zipper right now, but want to find Kate’s wisdom on the subject later? Here’s how to save this article in your MDK account with one click. Want to try your hand the great zippered design Kate is wearing? Take a look at her design The Wild One.