How to Replace Sofa Cushion Foam

If your sofa cushions have lost their shape and support, the fix is often simpler than you think — replace the foam. You don't need to reupholster the whole sofa or buy a new one. New foam can restore a sagging, flat sofa to like-new comfort in an afternoon. Here's how to do it.

What You'll Need

• Replacement foam: GoTo Foam 2" x 24" x 72" Firm Upholstery Cushion
• Batting wrap: PLANTIONAL Natural Cotton Batting
• Upholstery sewing kit: PLANTIONAL Upholstery Repair Sewing Kit, 47-Piece
• Electric carving knife or serrated bread knife (for cutting foam)
• Measuring tape

Why Replace Foam Instead of Buying New?

Quality sofa frames last 15–25 years, but foam typically breaks down in 5–10 years. If your sofa frame is solid but the cushions are flat and uncomfortable, replacing the foam is a fraction of the cost of a new sofa and takes just a few hours.

Step 1: Remove the Cushion Covers

Most sofa cushion covers have a zipper along the back or bottom edge. Unzip and remove the cover. If there's no zipper, the cover is sewn shut and will need to be carefully cut open along a seam, then re-sewn after the foam is replaced.

Step 2: Remove the Old Foam

Pull the old foam out of the cover. Note its dimensions — measure length, width, and height carefully. Also note the foam density — if the original foam was very firm, you'll want to match that. If it was too soft (which is why you're replacing it), go one density level firmer.

Step 3: Choose the Right Foam

GoTo Foam is available in multiple densities and thicknesses. For sofa seat cushions, a firm (43 ILD) foam gives the best support and longevity. For back cushions, a softer foam is more comfortable. Cut the foam slightly larger than the original — about 1/2 inch larger on each dimension — so it fills the cover fully and doesn't shift.

Step 4: Cut the Foam to Size

Use an electric carving knife for the cleanest cuts — it slices through foam like butter. A sharp serrated bread knife also works well. Mark your cut lines with a marker before cutting. Cut slowly and steadily for straight, even edges.

Step 5: Wrap with Batting (Optional but Recommended)

Wrap the cut foam with a layer of cotton batting and secure with spray adhesive. This gives the cushion a softer, more rounded appearance and helps it slide into the cover more easily. It also adds a layer of comfort on top of the firm foam.

Step 6: Insert into the Cover

Fold the foam in half lengthwise (like a taco) to make it easier to insert into the cover. Once partially in, unfold and work it into the corners. The foam should fit snugly — if it's too loose, the cushion will look flat and shift around.

Step 7: Close the Cover

Zip the cover closed. If the cover was cut open, use the upholstery sewing kit to hand-stitch the seam closed with a slip stitch for an invisible finish.

Pro Tips

• Order foam slightly larger than your measurements — it's easier to trim down than to deal with foam that's too small.
• High-resilience (HR) foam lasts longer than standard foam and is worth the extra cost for seat cushions.
• For L-shaped or custom cushions, trace the old foam onto the new foam before cutting.
• If the cushion cover is worn or stained, consider replacing it at the same time as the foam.
• Allow new foam to fully expand for 24 hours after unboxing before inserting into covers.