Seat Foam: A Buyer's Guide to Types, Thickness & Density

Seat foam is the foam used inside the seat cushions on sofas, armchairs and similar furniture. It usually comes as foam seating blocks or thick seating foam sheets, and is praised for being durable and good quality at an affordable price. It's available in a range of thicknesses and densities to suit personal taste.

Seat foam is incredibly versatile and resistant to wear and tear, which makes it a popular choice for sofas and armchairs in busy households.

What type of foam is used for seats?

Seat foam is also known as upholstery foam, and is an open-cell polyurethane foam. Most seat foams are medium to high density to ensure adequate support, though softer foams are also available – these are usually used in children's seats, such as mini armchairs.

There are various grades of seat or upholstery foam. When labelled this way, you can be confident the foam is fire retardant and of an appropriate density for proper support and comfort.

How thick should seat foam be?

Most domestic seats, such as those on sofas and armchairs, use medium-density seat foam. Medium foam offers the right level of comfort for seat pads that are at least 10cm thick, and is usually a great replacement for seat pads that were once filled with fibre.

High-density seat foam is much firmer and is typically used for thinner seat cushions – for example, in dining chair seat pads and in soft furnishings found in caravans and boats. It is not recommended for domestic seating over 10cm thick, where it will feel too hard.

How to order the right seating foam

Choosing the right seating foam comes down to both personal preference and the intended application. For a sofa or armchair foam cushion replacement, a medium-density foam is a good option. Those who want a more luxurious feel sometimes add a thinner memory foam pad on top of their seating foam block, though this must be accounted for in your measurements when ordering. For other applications, high-density seating foam is great where a thinner pad is required, as it still achieves the right level of comfort in a much thinner product.

If you'd like to see the main upholstery foam grades compared side by side, from softest to firmest, before you choose, our first-time buyer's guide to foam cut to size sets them all out.

How to replace a foam seat cushion

Replacing a foam seat cushion is very easy. Remove your old foam piece and measure its width, depth and height. As it is likely to be slightly flattened or misshapen, also measure your outer fabric cushion cover, and add at least 1.5cm to your recorded thickness to ensure there is adequate space. Then order your foam online via our cut to size tool, along with appropriately sized stockinette. Once it arrives, simply slip the foam into your cover.

Frequently asked questions

What foam is used for seat cushions?

Seat foam, also known as upholstery foam, is an open-cell polyurethane foam. It is usually a medium to high density to give adequate support, though softer grades are available, for example for children's seats.

How thick should seat cushion foam be?

Most domestic sofa and armchair seats use medium-density foam at least 10cm thick. Thinner cushions, such as dining chair pads and caravan or boat seating, use firmer high-density foam.

What density foam is best for a sofa seat?

For a sofa or armchair cushion replacement, medium-density foam is a good choice. For a more luxurious feel, you can add a thin memory foam pad on top, but remember to account for it in your measurements.

How do I measure to replace a seat cushion?

Remove the old foam and measure the width, depth and height of your fabric cover. Add at least 1.5cm to the thickness for a snug fit, and measure the cover rather than the old foam, which may have flattened or lost shape.

Can seat foam be cut to size?

Yes. You can order seat foam cut to size online to your exact dimensions, along with stockinette to help it slip into the cover.