Upholstery Foam Guide: Density, Firmness and Which Foam Your Cushions Need

Density vs Firmness: The Two Numbers That Actually Matter

These are the two figures worth knowing before you buy or reorder foam, and they are not the same thing. Density, quoted in kilograms per cubic metre (kg/m3), measures how much foam material is packed into the block. It is the single best predictor of how long a cushion holds its shape. Firmness, quoted in Newtons (N) or as an ILD/IFD rating, measures how hard the foam feels to sit on.

Not sure which job you need? Our guide to reupholster vs recover vs slipcover explains the difference, the cost order, and how to decide.

A common and expensive mistake is choosing foam on firmness alone. A low-density foam can be made to feel firm at first, but it collapses quickly because there is little material to support the load. A seat can feel identical in a shop and yet last three years or thirty depending on the density underneath. Density is what you are paying for.

• Density (kg/m3) sets durability and lifespan.
• Firmness (Newtons / ILD) sets how soft or hard it feels.
• You choose firmness for comfort; you choose density for how long that comfort lasts.

What Foam Density Do You Need for Seat Cushions?

For a seat cushion in an everyday Australian household, use a high-resilience (HR) foam of at least 32 to 35 kg/m3. Seats take the hardest, most repetitive load in the room, so this is the one place never to economise. Backs and scatter cushions can use lighter foam because they carry far less weight.

Density guide by use

• Builder-grade / bedding offcut (16 to 23 kg/m3): what cheap flat-pack seats ship with. Goes soft and hollow within one to three years. Avoid for any seat you sit on daily.
• Standard domestic seat (28 to 32 kg/m3): acceptable for light-use or occasional seating.
• High-resilience main seat (32 to 38 kg/m3): the correct choice for an everyday sofa or armchair. This is where Dunlop HR35 sits.
• Commercial / contract (38 kg/m3 and up, often fire-rated): for venues, waiting rooms and hospitality seating in constant use.

Firmness is then chosen on top of density to suit the sitter. A firm seat supports better and is easier to rise from, which many older sitters prefer; a medium seat feels plusher. Both can be built at the same durable density.

What Is Dunlop HR35 and Why We Use It

Dunlop HR35 is a 35 kg/m3 high-resilience foam made in Australia and carrying a 10-year warranty. We rebuild seat cushions in HR35 as standard, in a firm feel rated around 200 Newtons or a medium feel around 165 Newtons, then wrap the block in Dacron polyester so the cushion sits rounded and full rather than square and hard-edged.

High-resilience foam recovers its shape faster and more completely after each use than conventional polyurethane foam of the same firmness, which is why it keeps a seat looking full for years instead of developing a permanent bottom-shaped dip. The 35 kg/m3 density is the reason the warranty can run to a decade; density, not firmness, is what a foam warranty is really underwriting.

Why Did My Cushions Go Flat, and What Foam Fixes It?

Cushions go flat for one of two reasons: the foam has fatigued and lost density, or the support underneath (the webbing or springs) has given way and the foam is now bottoming out onto the frame. A foam-only refresh solves the first; a rebuild of the seat base solves the second, and many tired seats need both.

If the covers are still sound, replacing just the foam inserts is one of the most cost-effective repairs we do. We cut new high-resilience foam to the exact size of your existing cover, wrap it in Dacron, and refit it, so the seat feels firm and full again while the fabric you already have stays in place. There is more on this on our cushion refoaming and sagging sofa repair pages.

Seat, Back and Scatter: Different Foams for Different Jobs

A well-built piece rarely uses one foam throughout. Each part of the cushion set does a different job and calls for a different density and firmness.

• Seat cushions: high-resilience foam, 32 to 38 kg/m3, firm or medium, Dacron wrapped. The hardest-working part.
• Back cushions: a softer, lower-density foam, or a foam core with a fibre or feather wrap for a relaxed lean.
• Scatter and lumbar cushions: soft foam or fibre fill, chosen for feel rather than load.
• Tight-upholstered backs and arms: firmer foam bonded to the frame, sometimes over a felt or Dacron layer to soften edges.

How Long Does Upholstery Foam Last?

Quality high-resilience seat foam at 32 to 38 kg/m3 typically lasts 10 to 15 years or more of everyday use before it needs replacing, which is why Dunlop HR35 can carry a 10-year warranty. Builder-grade foam under 23 kg/m3 often softens noticeably within one to three years.

Lifespan depends on density first, then on how the piece is used: a main sofa used every evening fatigues faster than a formal-lounge chair, and a single favourite seat on a modular often goes before the rest. When one cushion has collapsed and the others feel fine, the density of the original foam is usually the reason.

Fire-Rated and Commercial Foam

Foam for cafes, restaurants, clubs, offices and other public venues is specified differently from domestic foam. Commercial seating generally requires higher-density foam (38 kg/m3 and up for constant use) and, importantly, foam and fabric that meet the relevant Australian fire-safety standards. Domestic foam carries no such obligation, so a residential-grade cushion is usually not suitable for a licensed venue.

If you are fitting out or recovering venue seating, confirm the fire rating of both the foam and the cover before ordering. There is more on compliance on our fire-rated commercial upholstery and commercial banquette seating pages.

Can You Just Add Foam or Dacron to a Soft Cushion?

Sometimes, yes, and it is worth asking before committing to full replacement. If the foam core is still sound but the cushion has lost its rounded shape, adding or renewing the Dacron wrap can plump it back up cheaply. If the foam itself has fatigued and lost density, no amount of wrap will fix it and the core needs replacing. Send a photo and tell us how the seat feels to sit on, and we will tell you honestly which of the two it is rather than selling you the bigger job.

Using Your Own Fabric (COM)

COM means "customer's own material", where you supply the fabric and the workshop does the upholstery. It suits people who have found a specific designer or specialty fabric. Before buying COM, check the fabric is upholstery-weight and suitable for the piece, confirm the metreage required with your upholsterer first, and ask about the fabric's rub count and any backing needs. A good workshop will tell you honestly if a fabric you love is not durable enough for how you plan to use the piece.

A Local Example of These Criteria in Practice

Weighing rub count, fade resistance, fibre type and fire rating is exactly the kind of judgement a specialist workshop makes daily. Dylberry Design, a family upholstery and furniture-restoration workshop in Eltham North servicing Melbourne, is one example of a business set up around this. It runs an in-house team, including a machinist, upholsterer and restorer, with around 100 years of combined craft, carries a broad fabric range, and gives honest advice on what will actually last in your home rather than pushing a single option. It holds a 5.0 rating from 44 Google reviews, offers free quotes from a photo, and prices each job individually and fairly on its scope and materials. The wider point is that the best fabric is the one matched to your piece, your room and your household, so it is worth talking through before you commit.

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