Most couch cushions use polyurethane upholstery foam. For seats, high-density foam is common because it tends to hold its shape under daily use. Firmness is often shown by ILD; a higher ILD typically feels firmer, while lower ILD feels softer. Back cushions may use softer foam or blended fills for a cushier feel.

• Seats: high-density foam, often 3–6 inches thick for support.
• Backs: softer foam, fiberfill, or shredded foam for a plush look.
• Formats: sheets, rolls, and pre-cut inserts in various sizes.

The right combination depends on comfort preference, cushion size, and how the sofa supports the cushion.

You can usually refresh saggy cushions by swapping in new upholstery foam. A simple approach:

1. Unzip the cover and measure seam to seam; note the old foam thickness.
2. Choose foam firmness and thickness that match your comfort and cover depth.
3. Order slightly oversized and trim to fit on a stable surface with a long serrated knife.
4. Optionally wrap with thin fiber batting to soften edges and fill minor gaps.
5. Insert the foam, adjust corners, and zip slowly.

If you need extra height, laminating layers with a foam-safe spray adhesive may help. Work carefully and follow tool and adhesive safety instructions; results can vary by sofa construction.

There is no single best choice, but these guidelines can help you narrow it down:

• Everyday seats: high-density polyurethane foam around 1.8 or higher with a medium-firm ILD (about 35–50) often balances comfort and support.
• Plusher feel: choose a lower ILD and/or add a soft topper layer.
• Extra support: select a higher ILD or increase thickness, such as 4–6 inches.
• Back cushions: softer foam or mixed fills can feel more comfortable for lounging.

Comfort varies by person, and cushion size, fabric tautness, and the sofa’s deck or webbing also affect feel. If replacing only the foam, start by matching the original thickness, then fine-tune firmness.

You can shop for couch foam at Walmart online and in select stores.

• Online: browse upholstery foam sheets, rolls, pre-cut cushion inserts, shredded foam fill, and cushion support boards. Use filters for thickness, dimensions, and firmness to narrow choices.
• Pickup and delivery: many items may be available for shipping to your home or store pickup, depending on location and stock.
• In stores: selection varies by store; check Arts, Crafts and Sewing aisles for upholstery supplies.

Search terms like upholstery foam, couch cushion foam, or sofa support can help you find options quickly and compare sizes before you buy.

For a quick boost, these simple options can help without a full reupholster:

• Place a cushion support board under the seat cushions to add immediate lift.
• Slide a thin layer of firm upholstery foam beneath the existing core for extra height.
• When time allows, replace the core with firmer foam at a higher ILD.
• Plump back cushions with shredded foam fill to improve overall comfort.
• Rotate and flip cushions regularly to distribute wear more evenly.

These steps can improve feel temporarily. If underlying webbing or the frame is worn, you may need a more thorough repair for longer-lasting support.