Fix Sagging Couch Cushions

Cushions fail gradually, then all at once. You notice the sag first when you sit down harder than you meant to, when the coffee table suddenly feels closer, when getting up requires a little push from the armrest. Most couch cushions contain polyurethane foam that compresses permanently over time, losing twenty to thirty percent of its thickness in the first few years. The fabric cover stays intact while everything underneath collapses into a soft divot that maps exactly where you sit. Fixing sagging cushions is less about the couch and more about understanding what foam does under load. You are essentially rebuilding the support structure inside an existing shell, and the work takes an afternoon once you understand the anatomy of what failed. The repair depends on whether your cushions have removable covers with zippers. Most modern couches do. The goal is to add back the height and firmness the foam lost, either by layering new materials on top of old foam or replacing it entirely. You can restore a couch that feels ten years old to something that sits like new for under a hundred dollars in materials. The work happens on the living room floor with scissors and a stapler, and the difference when you sit down afterward is immediate.

1. Measure What You're Fixing. Unzip each cushion cover and pull out the foam core. Measure the foam dimensions precisely — length, width, and current compressed thickness at the center where the sag is worst. Note how much thickness the foam has lost by checking the edges, which typically compress less. Write down these measurements for each cushion.
2. Pick Your Rebuild Strategy. If the existing foam is still somewhat firm at the edges, add a two-inch high-density foam topper and wrap everything in dacron batting. If the foam crumbles when squeezed or has permanent deep creases, replace it entirely with new high-density foam cut to match original dimensions. For back cushions that only need slight help, a layer of batting alone often suffices.
3. Cut Foam Cleanly. Use an electric carving knife or long serrated bread knife to cut foam in one smooth stroke. Measure twice, mark the cut line with a marker, and cut on a flat surface with the foam fully extended. For layered repairs, cut the topper foam slightly larger — a quarter-inch oversized on each dimension — so it fills the cover fully when compressed.
4. Wrap and Secure Batting. Unroll dacron batting on the floor and place your foam stack in the center. Wrap the batting around the foam like wrapping a gift, pulling it snug but not tight. Trim excess batting and secure the seam with three or four pins or a few staples from a light-duty stapler. The batting prevents foam from gripping the fabric cover and creates a fuller, softer surface feel.
5. Stuff Covers Back Up. Fold or roll the wrapped foam to fit through the cover opening, then work it into position inside. Distribute the foam evenly, pushing into corners and smoothing out wrinkles from inside the cover. The foam should fill the cover completely without bulging seams. If the foam is significantly thicker than original, you may need to compress it firmly as you zip.
6. Shore Up the Frame. For couches where the entire platform sags beneath the cushions, cut half-inch plywood to fit the seating deck between the arms. Slide it under the cushions on top of the existing webbing or springs. This creates a firm base that prevents the cushions from sinking into a hammock shape. Sand the edges smooth to avoid snagging fabric.
7. Break In Your Repair. Place cushions back on the couch and punch them firmly several times to distribute the foam and batting evenly. Sit in your normal spot and shift your weight to compress the new foam into its working shape. The cushions will feel firm initially and will soften slightly over the first week as the foam takes a set.
8. Protect Your Work Long-Term. Check zipper function and ensure all covers are fully closed with sliders at the end of the zipper track. Brush or vacuum covers to remove any loose batting fibers. Set a reminder to flip cushions monthly going forward. Properly maintained high-density foam should hold its shape for five to seven years before needing attention again.