- Metal zipper, at least 12"
- Exterior and lining fabric, at least 13.5" x 24" and a bit more for zipper binding
- Fabric for binding
Cut both your interior (lining) and exterior fabric to 13.5" x 24".
You'll need to cut your zipper (with it zipped) to 11.5". This is fun with a metal zipper. Do it carefully and with your worst scissors.
Next, you'll make the binding for the ends of the zipper.
Cut two pieces of fabric 2" x 3.5" or so, I like to have it a little long while I'm working. Create the binding by folding each piece in half lengthwise, pressing, and then unfolding. Fold each edge towards the middle crease you've just created, just shy of the crease and press. You'll end up with the v-like pieces in the left picture, below.
Open the strip back up and line up one long-side raw edge of the binding with the raw edge of the zipper, right sides together. Pin in place and stitch along the first crease (c). After this you'll see the binding nicely wraps around the edge of the zipper. Slip stitch the reverse edge (a) to the zipper. When you've finished both ends it will look like the wide, middle image below.
When you've completed both sides of the fabric, lay your piece flat with the zipper at the top and inside out. Pin the layers in place and stitch along the opens sides just on the outside of where the zipper ends. Then clean up your raw edges, leaving a generous a 1/4 of an inch beyond the stitching.
Finally, flip it inside out and press it all nice. You're done! Throw it in your bike box!