Outdoor Box Cushion

My giant awesome Stormtrooper adirondack chair needed a cushion. I picked up some 3" thick cushion foam at Joann's and got to work.

The finished cushion size is 26" x 26" x 3". This is two panels (top and bottom) and a gusset with a zipper at the back.


  • 2 Top/Bottom Panels cut 27" x 27"
  • 2 Zipper Gusset Panels cut 30" x 2"
  • 1 Front/Sides Gusset Panel cut 80" x 4"
  • 1 30" zipper
  • Seam stick/basting tape (optional but helps)

I used Sunbrella canvas and used my Sailrite Edge hot knife to cut all pieces so that they wouldn't unravel.

I started with the zipper gusset. Take one of the 30" x 2" pieces and place it right side down on top of the zipper flange (zipper facing up). Sew. Fold the placket back on itself and topstitch. Repeat for the other piece.

Next, join the long gusset panel to the zipper panel. Right sides together, sew along one of the short ends at 1/2" or so (mine was probably more like 1/4"). Topstitch on the right side, pushing the seam away from the zipper and toward the long side. Repeat for the other side and you have a big tube. Fold the zipper part in half, matching up the seams, and mark a notch at the center. Do the same for the long end, marking the center that will be the front of the cushion.


Take one of the square panels. Fold it in half to cut a little mark at the center of what would be the front and back. I did not mark the center on the sides because that wasn't going to matter.

Using a can, I rounded the corners to make it a little easier to turn the gusset.


Starting at the center mark on what would be the rear of the cushion, apply seam stick tape to the wrong side of the panel and go slightly around the corner. Repeat for the other side. Remove the transfer tape and baste the zipper panel (right side down on the right side of the panel) starting at the center mark and just slightly around the corner. To get around the corner, I cut little notches (no more than 1/4") to help it lay flat around the corner. I then sewed that basted area down, using a 1/2" seam allowance, and stopping before I reached the seam at the end of the zipper panel (there's a reason for this).


Next, apply seam stick starting at the front center notch of the cushion panel, around the corner and up the side to where it meets the zipper portion. Repeat for other side (starting at the center and working around the other corner/side).

Place the front center mark of the gusset on the front center mark of the cushion and baste it down, taking care around the corners. When reaching the seam on the gusset where it's joined to the zipper, there should be an inch or so extra. Fold that over so goes a bit past the zipper, this will take up the slack and provide a little hiding spot for the zipper on the outside.


Sew it down.

OPEN THE ZIPPER. If you don't open the zipper now, it's going to be a bitch to open it later.

Repeat the same process to attach the gusset to the other panel. 


Turn it right side out and jam the cushion in there!

My cushion size was a bit bigger than the foam, so I had to do a little doctoring to make it happen. The width of the foam was only 24" so I got a little extra on the length and cut an extra 2" strip (plus a small block to fill a corner) and used adhesive spray to stick it on to create my 26" x 26" square cushion. To hide the seams, I used dacron cushion wrap (also used the adhesive spray to keep that on). 

I can now sit on my glorious Stormtrooper chair with a comfy tush.

Front view

Front view

Back view

Back view