I offered to make a cushion to turn a small chest into a seat for an apartment. The chest has a rim along the back and two sides so the cushion was designed to fit in this space.
I constructed it in my head a couple of times and then started whacking away at 2-inch foam and some upholstery fabric. I had two white zippers in my stash and made them work by coloring the tape with Copic markers and stitching them end to end. They meet in the center of the back.
I made the construction like a box so there is a seam at every edge of the foam.
Here you can see the zippers where they meet
The zipper is hidden by a placket. Too many waves in the placket for me but it was difficult getting the sturdy zipper tape and the slippery fabric to play nicely together. It will be on the back of the cushion anyway.
This is a better color rendition than the first photo of the whole cushion. We'll blame that on the shiny fabric.