I’ve had a lot of trouble with zippers. They buckle, the two sides don’t come out even so seams and stripes don’t line up the way they should, and I can never figure out what to do with that little extra bit at the top. But I’ve been getting better at them. It’s been a few years since I had any really lumpy zippers (if your zippers are lumpy, you’re pulling on the fabric too much), and I’m getting better at lining up the two sides. And recently I learned how to put in an invisible zipper correctly.
The trick to getting your invisible zipper to actually be invisible is to press it out first. The invisible zipper folds over when it’s zipped, pulling the teeth behind the fabric. If you sew it in folded up, you can’t sew very close to the edge, because the teeth get in the way. But if you unzip the zipper, you can turn the teeth toward the center. This lets you sew right up at the edge of the fabric part of the zipper, so when you close the zipper and the teeth spring back, the fabric comes all the way to the edge and looks like a seam.
This means you really can’t sew in the zipper when it’s closed, so you’re not going to be able to sew to the very bottom of the zipper (because the bit you pull on to close it will get in the way). Just get one that’s a little longer than you need and add a stitch where you want the bottom of the zipper to be.
If that doesn’t make sense, here are step by step directions.
1) Unzip the zipper and press the teeth toward the center
2) Sew your fabric to the zipper, as close to the teeth as you can get (if you have a zipper foot, this is easy. If you lost your zipper foot and never think to buy another when you’re in the store, be careful not to sew over the teeth). Sew as far down as you can before you hit the bit that closes the zipper, then stop.
3) Sew the other side the same way.
4) Close the zipper and sew up the rest of the seam.
5) Sew around the zipper where the bottom of the zipper meets the seam.