How to Make a Cozy Seat Cushion for a Built-In Bench

Do you have a nook, window seat or built-in bench that would be a lot cozier with a seat cushion? Pick up some thick upholstery foam and your favorite fabric to make a comfortable DIY cushion.

For a no-sew option, you could staple fabric around foam and a piece of plywood, upholstery style. But in this case I wanted more of a square, boxy look, with a removable fitted-sheet style cover. Here’s how it’s done.

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DIY Seat Cushion

Materials

• Upholstery foam, 4-inch or thicker (I used this foam)
• Fabric marker
• Straight edge (a carpenter’s square or quilting ruler is ideal)
• Bread knife or box knife
• Fabric
• Sewing pins
• Sewing machine
• Iron
• Half-inch elastic
• Elastic threader or safety pin
• Plywood (optional)

Spoonflower has endless fabric options in all sorts of mid-century modern patterns. I picked bruxamagica’s Vintage Kitsch Stick Blue in the 56 x 72-inch size with cypress cotton canvas material to tie in with my turquoise curtains and tiki bar.

1. Cut the Upholstery Foam

Start by cutting the upholstery foam to the exact size of your nook or bench area.

Use a marker to draw a line where you want to make the cut. A large carpenter’s square can help you get a clean straight line.

There are different ways to cut upholstery foam. We used a box knife and made straight cuts in one direction, over and over until the foam gradually cut down.

Some people recommend using a bread knife. This tutorial may help.

2. Cut the Upholstery Fabric

Next, center your foam cushion over the fabric to mark out the cuts. You’ll want to cut four squares out of the fabric corners, right up to the tips of the cushion corners as shown below.

If you have one of these square quilting rulers, that will make it very easy to mark your cuts. Otherwise you can use a carpenter’s square or other square shape to guide your fabric marker.

Then cut out the corners, so your fabric looks like this…

These 9.5-inch fabric flaps will cover the 4-inch height of the foam, leaving 5.5 inches to create the fitted elastic section under the cushion.

3. Sew the Seat Cushion Corners

Now pin and sew all four of those corner seams. Bring the right sides of the fabric together, leaving the wrong sides facing out.

Giving it a quarter-inch seam will provide tight, fitted corners around the foam cushion.

I sewed a quarter-inch seam, then went over the frayed edges with a zigzag stitch to contain them.

Look at that corner! Making clean square cuts in step 2 will give you a nice square corner here in step 3.

4. Sew the Elastic Casing

Now your upholstery fabric is shaped like a box, so you’ll need an elastic casing to tighten it around the cushion.

Fold over a quarter-inch of fabric all around the perimeter and iron it flat. Then fold over an inch more, or enough to fit your elastic, and iron that down.

Pin that casing in place and sew almost all the way around, making sure to leave space in the casing for the elastic, as well as leaving a couple of inches unsewn where you can insert the elastic.

5. Add Elastic to the Seat Cushion Cover

Next you’ll insert the elastic into the casing and pull it tight to create the fitted cushion cover. An elastic threader can be a big help, especially if you’re using thick upholstery fabric. But a large safety pin will work in a pinch.

Attach the threader or safety pin to one end of the elastic, and thread it all the way through the casing. It also helps to have a lot of extra elastic so you have some slack.

Once the elastic is through, you might want to tie the ends together to keep them from disappearing into the casing. Then pull the elastic nice and tight until you get the fit that you want for your cushion.

Finally, sew the elastic ends together and cut off the excess. I sewed back and forth over the ends several times to keep them from snapping loose. Then finish sewing the casing shut.

Add the cushion cover over your upholstery foam and set it onto your bench or nook area. Here’s how the corners look with this method.

It’s not quite as square as I was hoping for. Since upholstery foam isn’t as sturdy as, say, a mattress, the foam gets pulled in a bit around the corners.

For a boxier look, you could try cutting a piece of plywood the same size as your foam cushion. Place the plywood under the foam, and wrap the cover around the foam and plywood to provide a sturdy surface with square corners.

Cozy Built-In Seat Cushion

The cats tested our cozy nook right away. They are always looking for more areas to lounge. Here’s Charlie soaking up the catnip on the cushion.

I bought these pillow covers to go with my orange living room couch, but they ended up being perfect here instead. They tie in well with the modern pattern and colors of the cushion fabric.

This is also a great spot to add some retro posters. A couple of vintage posters of Disney’s New Orleans Square coordinate with the nautical look of our adjacent tiki bar. And of course, I had to add some cat art!