Upholstery foam is the polyurethane foam inside sofa seats, back cushions and armchairs. When it sags, crumbles or stops springing back, fitting new foam restores the support and keeps a good frame and cover in use for longer.
iFoam cuts upholstery foam to size at its Cape Town and Durban branches. This guide covers the types of upholstery foam, how to measure your covers and how to re-stuff a sofa or armchair step by step. For density and firmness in more depth, see the guide to high-density foam for couch cushions.
What Is Upholstery Foam?
Upholstery foam is open-cell polyurethane (PU) foam. Its cells are connected, so air moves through as you sit down and get up. That lets the foam breathe and recover its shape thousands of times.
Three foam types come up in upholstery:
- Standard polyurethane foam: The everyday choice for most home sofas and chairs, made in a wide range of densities.
- High-resilience (HR) foam: A PU foam that springs back faster and more fully, which suits seats used every day and commercial seating.
- Memory foam: A slow-recovering foam that moulds to the body. It is better known in mattresses and toppers, and in sofa seats it is usually only a thin top layer, if used at all.
Foam wears out in two ways. It softens until you sink too far into the seat, or it takes a permanent set and no longer returns to shape. Either way, the foam needs replacing.
Choosing the Right Grade
Two measures decide how upholstery foam performs. Density, in kg/m³, sets how long the foam lasts. Firmness, often given as ILD, sets how hard or soft it feels.
| Position | Typical density | Notes |
|---|---|---|
| Seat cushions | 30 to 36 kg/m³ | Carries full body weight, so durability comes first |
| Back cushions | 22 to 28 kg/m³ | Lighter load, often softened with a Dacron wrap |
| Occasional chairs | 18 to 22 kg/m³ | Fine for light use, not for daily seating |
Density and firmness are separate. A dense foam can still feel soft, so ask for both when you order. The foam density chart explains the grades in more detail.
Myth: Higher-density foam always feels harder.
Reality: Density sets durability, while firmness sets the feel. A dense foam can be made soft and still last for years.
Key principle: upgrade the seat foam rather than copying the old foam. If the original went flat quickly, it was probably too light for the job.
How to Measure Cushion Covers
Wrong measurements are the main reason a re-stuffed cushion looks baggy or will not close. Measure the inside of the cover, not the outside of the old cushion.
- Remove the cover: Unzip the cover and take out the old foam.
- Measure inside the cover: Note the internal width, depth and thickness in millimetres.
- Allow a little extra: Foam should be slightly larger than the cover so the cushion looks full, so ask how much to add for your cover and foam grade.
- Template odd shapes: Trace L-shaped, T-shaped or angled cushions onto paper and send the template with your order.
- Check the closure: A zip lets you fit a snugger cushion than a sewn edge.
Photograph the old foam before you throw it away. Notches and shaped edges are easy to forget.
Step by Step: How to Re-Stuff a Sofa or Armchair
This method suits cushions with zipped covers on a sofa or armchair.
What You Need
- New foam: Cut to size for each cushion.
- Cutting tool: An electric carving knife gives the cleanest cut if you need to trim.
- Dacron wrap: Optional, for a softer and fuller finish.
- Spray adhesive: Optional, to hold the Dacron in place.
- Thin plastic: A large bag or cling wrap makes it far easier to slide foam into the cover.
- Tape measure and marker: For checking sizes before trimming.
Steps
Step 1: Remove the old foam. Unzip the cover, pull out the old foam and note how it sat, including any notches or shaped edges.
Step 2: Clean the cover. Vacuum out crumbs of old foam, or wash the cover if the fabric allows. Let it dry completely.
Step 3: Check the new foam. Hold the new foam against your measurements before cutting anything.
Step 4: Trim if needed. Use an electric carving knife for straight, clean cuts. Scissors tend to tear denser foam.
Step 5: Add Dacron if you want it. Wrap the foam in Dacron and fix it lightly with spray adhesive at the edges so it does not bunch.
Step 6: Slide the foam in. Put the foam inside a plastic bag or wrap it in cling wrap, then feed it through the zip opening. The plastic stops the foam dragging on the fabric.
Step 7: Remove the plastic and set the foam. Pull the plastic out through the opening, then push the foam into all four corners.
Step 8: Zip up and test. Close the zip, sit on the cushion and check for even support with no soft corners.
Step 9: Repeat for every cushion. Use the same grade and size for each seat cushion in the same piece, so the seats feel even.
New foam can feel firmer than expected for the first week or two. It softens slightly as it settles.
Dacron Wrap: A Softer Feel and Fuller Look
Dacron is a polyester fibre layer wrapped around the foam before the cover goes on. It rounds off the edges and softens the first feel of the cushion without changing the foam underneath.
It works best on back cushions, scatter cushions and arms. It is not a substitute for foam in a seat, because fibre flattens under body weight and does not recover.
Foam for Outdoor Cushions
Standard upholstery foam soaks up water and dries slowly, so it is a poor choice for cushions left outside. For patio and boat cushions, closed-cell PE or EVA foam sheet does not absorb water. Pair it with a weather-resistant cover.
Key Terms Explained
Upholstery foam: Open-cell polyurethane foam used in sofas, chairs and cushions. It recovers quickly after each use.
Density (kg/m³): The weight of one cubic metre of foam. Higher density means more material and a longer working life.
ILD: A firmness rating showing how much force it takes to press the foam down by a set amount. Lower numbers feel softer.
High-resilience (HR) foam: A polyurethane foam that springs back faster and more fully than standard foam. It suits seats used heavily every day.
Permanent set: When foam stays flattened after use instead of recovering. It is the clearest sign the foam has reached the end of its life.
Dacron: A polyester fibre wrap that softens the surface of a cushion and gives it a rounder shape.
Where to Get Upholstery Foam Cut to Size
iFoam cuts upholstery foam to size at its Cape Town and Durban branches for upholsterers, furniture makers and individual projects. Send the internal cover sizes, the cushion position and the feel you want, and the foam is cut to order. The guide to foam cut to size explains how ordering works.
Resources
- iFoam, foam cut to size.
- iFoam, high-density foam for couch cushions.
- iFoam, foam density chart.
- iFoam, open-cell vs closed-cell foam.
- iFoam, closed-cell foam sheets.
- ASTM International, ASTM D3574, test methods for flexible cellular materials.
Frequently Asked Questions
What density upholstery foam should I use for a sofa?
For seats used every day, 30 to 36 kg/m³ is a good starting point. Back cushions can be lighter, at around 22 to 28 kg/m³. Lighter foam suits only occasional seating.
Can I re-stuff a sofa myself?
Yes, if the cushions have zipped covers and you measure carefully. Fixed seats, stapled fabric and frame repairs are better left to an upholsterer.
How do I measure for replacement upholstery foam?
Take the width, depth and thickness from inside the cover, in millimetres. Make a paper template for odd shapes, and allow a little extra so the cushion looks full.
What is the difference between upholstery foam and memory foam?
Upholstery foam is springy PU foam that recovers quickly. Memory foam recovers slowly and moulds to the body, which suits mattress toppers better than sofa seats.
What is HR foam?
High-resilience foam is a polyurethane foam that recovers faster and more fully after you stand up. It is a good choice for seats that get heavy daily use.
Is high-density foam always firmer?
No. Density decides how long foam lasts, while firmness is set separately. A dense foam can still feel soft.
How do I know when sofa foam needs replacing?
Look for dips in the seat, cushions that stay flat after you stand up, or foam that crumbles when you open the cover. Sinking through to the base is a clear sign.
How do I get foam into a cushion cover?
Slip the foam into a large plastic bag or wrap it in cling wrap, slide it through the zip, then pull the plastic out. Push the foam into the corners before closing.
Can I use upholstery foam for outdoor cushions?
Standard upholstery foam absorbs water and dries slowly outdoors. Closed-cell PE or EVA foam is better for patio and boat cushions.
Is it cheaper to re-stuff a sofa than buy a new one?
Usually, yes, when the frame and fabric are still in good shape. New foam brings back the support for a fraction of the cost of new furniture.
Does iFoam cut upholstery foam to size?
Yes. iFoam cuts upholstery foam to size at its Cape Town and Durban branches, working from the internal cover measurements you supply.
Final Thoughts
Good upholstery foam turns a tired sofa back into a comfortable one. Match the density to the cushion position, measure the inside of each cover and fit the foam snugly, and the re-stuffed seats will last.
Contact iFoam in Cape Town or Durban with your cushion sizes to have upholstery foam cut to fit.