Foam Density Chart: Foam Firmness by Body Weight & Cushion Depth
A foam density chart helps you choose seat foam by matching two things: how heavy the user is and how deep the cushion is. Heavier users press further into the foam, so they need a firmer or deeper cushion, while lighter users often prefer a medium grade in deep seats. Density decides how long the foam lasts, and hardness decides how firm it feels. GB Foam Direct cuts every upholstery grade to size, so you can choose the grade that suits the person using the seat.
Key takeaways
- Density is weight per cubic metre (kg/m3), tested to BS EN ISO 845, and mainly affects how long foam lasts.
- Hardness is the force in newtons (N) needed to compress foam by a set amount, tested to BS EN ISO 2439.
- Heavier users compress foam further, so thin cushions need a harder grade to avoid bottoming out.
- GB recommends GB 39H for seat cushions up to 4 inches (10cm) and GB 41M for seat cushions over 4 inches (10cm).
- GB 42H Superior Hard, at 220 to 300 N, is GB’s grade for heavy use seating.
- GB Foam Direct has cut foam in High Wycombe since 1976, works to ISO 9001 and gives a 5 year guarantee against faults in manufacture.
How Does Body Weight Affect Foam Choice?
Body weight decides how far a person sinks into a cushion, so heavier users need firmer or deeper foam and lighter users can use softer grades.
When the foam compresses all the way, the sitter feels the frame or base underneath, which is called bottoming out. A heavier user reaches that point sooner on a thin, soft cushion. A lighter user may find a hard grade in a deep cushion feels stiff because they never compress it far enough to feel its give.
Body weight also affects how fast foam wears. Heavier or more frequent use breaks down foam cells sooner, which is why a higher density grade is worth it for a seat used every day by a heavier person.
What Is the Difference Between Density and Firmness?
Density is how much the foam weighs per cubic metre, while firmness is how hard it feels when you sit on it.
GB tests density to BS EN ISO 845 and hardness to BS EN ISO 2439. In ISO 2439, hardness is the force in newtons needed to press a 200mm indenter into the foam by a set percentage of its thickness, so a higher N figure feels firmer.
The two do not move together. GB 39S Luxury Soft and GB 39H Luxury Hard both have a density of 37 to 41 kg/m3, but GB 39S is 100 to 140 N and GB 39H is 180 to 220 N. The full specifications for every grade are in our high density foam guide, and our foam terminology guide explains other terms on datasheets.
Foam Density Chart by Body Weight and Cushion Depth
Use this chart to match the user and the cushion depth to a GB seat grade. These are suggestions based on our experience and feedback from customers over the years, not fixed rules. Personal preference for how a foam feels should always be taken into account, so a user who likes a softer or firmer seat can move one grade either way.
| User and Use | Seat Up to 4 Inches (10cm) | Seat Over 4 Inches (10cm) | Back Cushions |
|---|---|---|---|
| Lighter build, light use | GB 39H Luxury Hard | GB 41M Luxury Medium | GB 39S Luxury Soft |
| Average build, daily use | GB 39H Luxury Hard | GB 41M Luxury Medium | GB 39S Luxury Soft |
| Heavier build, daily use | GB 42H Superior Hard | GB 39H Luxury Hard | GB 39S Luxury Soft |
| Heavy use or several users | GB 42H Superior Hard | GB 42H Superior Hard | GB 39S Luxury Soft |
| Budget, occasional use | GB 33H Average Hard | GB 33M Average Medium | GB 33S Average Soft |
GB 33M is listed for seat cushions of 5 inches (12.7cm) or deeper, so choose GB 33H for Average grade seats between 4 and 5 inches.
Which Density Should You Choose?
Choose the density for how often the seat is used, then choose the hardness from the chart for who uses it.
| Use | Recommended Density | Why |
|---|---|---|
| Family sofa used every day | 37 to 43 kg/m3 (Luxury grades) | Fatigue class V for longer life |
| Heavy use or commercial seating | 38 to 42 kg/m3 (GB 42H) | Hardest grade at 220 to 300 N |
| Spare room chair or occasional seat | 31.4 to 34.7 kg/m3 (Average grades) | Lower cost, fatigue class S |
| Back cushions | 37 to 41 kg/m3 (GB 39S) | Soft feel with Luxury durability |
For seats in pubs, cafes and restaurants, see our contract bar seating range.
How to Choose Foam Firmness for Your Weight
To choose foam firmness for your weight, start with the user and the cushion depth, then pick the density and hardness.
Note who uses the seat. Write down who sits there most and whether they are lighter or heavier than average, because heavier users compress the foam further.
Measure the cushion depth. Measure the cover border height in inches or centimetres, because depth decides how much foam there is to support that weight.
Pick the density for the use. Choose a Luxury grade at 37 to 43 kg/m3 for daily use seats and an Average grade at 31.4 to 34.7 kg/m3 for light use or backs.
Pick the hardness from the chart. Match the user and the depth to a suggested grade in the chart above, then adjust for personal preference, going one step firmer for heavier users on thin cushions.
Consider a Dacron wrap. Add Dacron if you want a softer, rounded surface on a firm grade, as it adds about 1cm to the top and bottom.
Check with our team before ordering. Call or email us with the cushion sizes and who will use them, and we will confirm the grade before you place the order.
Our guide to measuring foam cushions shows where to measure the border height.
Mistakes to Avoid
- Judging firmness by density. A dense foam can still feel soft, so always check the hardness in newtons.
- Using a soft grade for seats. GB 39S and GB 33S are back cushion grades and are not recommended for seating.
- Choosing a thin, medium grade for a heavier user. Medium grades in thin cushions compress fully under more weight and bottom out.
- Copying the old foam. Old foam has softened and lost height, so it is not a reliable guide to the grade you need.
- Forgetting who else uses the seat. Choose for the heaviest regular user, or the cushion will wear unevenly.
If your cushions are already flat, our guide to fixing sagging sofa cushions explains the signs and fixes.
Why Choose GB Foam Direct?
GB Foam Direct has converted foam in High Wycombe since 1976, originally for the furniture trade, using CNC machines and experienced freehand cutters. Every one of our upholstery foam grades is tested for density and hardness and complies with the Furniture and Furnishings (Fire) (Safety) Regulations 1988.
We work to ISO 9001 and give a 5 year guarantee against faults in manufacture. Orders before 11am Monday to Thursday are eligible for next working day delivery, and Saturday delivery is available.
Speak to Our Team
If you need help choosing the right foam firmness for the people using your seats, call us on 01494 441177, email sales@gbfoam.com or fill out our contact form. We are in the office from 9am to 5pm Monday to Thursday and 9am to 3pm on Friday.
Foam Density Chart FAQs
What foam firmness should I choose for my weight?
Heavier users usually need a firmer or deeper foam so the cushion does not bottom out, while lighter users often find a medium grade more comfortable in deep cushions. For thin seat cushions up to 4 inches (10cm), GB Foam Direct recommends GB 39H, and GB 42H Superior Hard for heavy use. For deeper seats, GB 41M suits most users. These are suggestions based on our experience and customer feedback, and personal preference for the feel of the foam should always be taken into account.
Is 32 density foam good for a sofa?
Foam around 32 kg/m3 is suitable for a sofa with light to moderate use. GB’s Average grades, GB 33S, GB 33M and GB 33H, have a density of 31.4 to 34.7 kg/m3 and a BS 3379 fatigue class of S. For a sofa used every day, a Luxury grade at 37 to 43 kg/m3 will usually last longer.
Is 40 density foam good for a sofa?
Yes, foam around 40 kg/m3 is a good density for a sofa used every day. GB’s Luxury grades, GB 39S, GB 39H and GB 41M, sit at 37 to 43 kg/m3 and carry a BS 3379 fatigue class of V. Choose the hardness separately, because density alone does not decide how firm the foam feels.
Is high density foam firm or soft?
High density foam can be soft, medium or firm, because density and firmness are separate measurements. Density is weight per cubic metre and mainly affects how long the foam lasts. Firmness is measured as hardness in newtons, so GB 39S and GB 39H have the same density but feel very different.
What is the difference between foam density and firmness?
Foam density is how much the foam weighs per cubic metre, tested to BS EN ISO 845, and it mainly affects durability. Firmness is the hardness, tested to BS EN ISO 2439 as the force in newtons needed to compress the foam by a set amount. A dense foam can still feel soft.
What foam is best for a heavy person?
A heavier person is best suited to a dense, hard grade, such as GB 42H Superior Hard at 220 to 300 N, or a deeper cushion in a Luxury grade. Thin, soft cushions compress fully under more weight and wear out faster. Ask our team to confirm the grade for your cushion depth.
Does foam firmness change with thickness?
Yes, a thicker cushion feels softer than a thinner one in the same grade, because there is more foam to compress before you reach the base. That is why GB Foam Direct recommends a hard grade for cushions up to 4 inches (10cm) and a medium grade for deeper cushions. Back cushions use a soft grade at any depth.
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