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Foam firmness finder

Five questions. Where it lives, who sits on it, how you like to sit, how thick it can be, how often it's used. You get the foam I'd cut for you — and the reasons, in plain words.

Worked out by

The Weather Man of Casco Bay ·

The quick answer

Choose foam by two numbers, not one: density (lb/ft³ or kg/m³) decides how long it lasts, firmness (indentation hardness) decides how it feels. Everyday indoor seats suit high-resilience foam around 1.9–2.2 lb/ft³ (30–35 kg/m³) at 3–4 in; heavier sitters need a higher density or more thickness; outdoor cushions need open-cell dry-fast foam that drains.

The foam firmness finder

Every field is live. Change a number and the drawing redraws; copy the link and it opens with your numbers.

1. Where will the cushion live?
2. The heaviest regular sitter
3. How do you like to sit?
4. Thickness

Pick one only if a sill, table or drawer limits the height.

5. How often is it used?

Load an example — the ones marked are past projects

Drawing…

Cross-section to scale: cover, wrap, foam core and what sits under it — and roughly how far it gives.
Get a quote with these numbers

Buyer questions

  1. A common question

    What foam do you use, how firm is it, and is it wrapped in Dacron?

    The workshop's answer

    About 2.0 lb/ft³ (32 kg/m³) high-resilience foam — firm to medium-hard and long-lasting, so you don't sink in. It is wrapped in polyester fiber (Dacron) before it goes into the cover, for fuller, softer edges.

  2. A common question

    Do you have high-density foam, 1.8 lb or more, 6 inches thick, so adults won't sink through?

    The workshop's answer

    Yes: the foam is about 2.0 lb/ft³ (32 kg/m³), so it meets 1.8 lb. It sits in the firm category — there is no official ILD figure to quote — and a 6 in thickness can be made.

  3. A common question

    Can I get a softer, sink-in sofa feel instead of a firm bench cushion?

    The workshop's answer

    Yes. The standard 2.0 lb (32 kg/m³) foam is medium-firm; a softer 1.75 lb (28 kg/m³) foam sits noticeably plusher, with a slight sink-in character, and gets the same fiber wrap. Ask for it by name in the order note.

  4. A common question

    Do you have quick-dry foam? We get hot summers and snowy winters.

    The workshop's answer

    No — and the workshop said so plainly. The outdoor fabric is UV-resistant and water-repellent, but the foam is not quick-dry: the cushions suit a covered porch or winter storage, not open rain and snow.

  5. A common question

    Are the back cushions the same foam as the seat?

    The workshop's answer

    No. Back pillows are filled with shredded foam, softer to lean against; seats use solid foam.

A real project

Soft sofa, firm facts

Two cushions, 41 by 26 inches, 5 inches thick, for a new sofa frame. The owner wanted to sink in, not perch, and asked whether thicker Dacron or extra fiber layers would do it.

They wouldn't, friend. Wrap softens the edges, not the seat. The workshop changed the foam instead: its softer 1.75 lb (28 kg/m³) grade in place of the standard 2.0 lb, same wrap, same thickness — three words in the order note.

The lesson: for lounging seats, change the foam, not just the thickness. Then check the density; softness bought with a very low grade wears out first.

How to use it

  1. Say where it lives

    Bench, window seat, dining, floor, outdoor or sunbed. The place sets the starting thickness and whether the foam must drain.

  2. Name the heaviest regular sitter

    Not the average. The one who drops in hardest every day decides the firmness.

  3. Be honest about how you sit

    Upright and firm, somewhere in the middle, or soft with a little sink. Soft usually means a soft top over a firm base.

  4. Give a thickness if the space limits you

    Window sills, tables and drawers under the seat all cap the height. Otherwise let the finder choose.

  5. Read both numbers

    Density for the years, firmness for the feel. Ask any maker for both — one number is half a spec.

  6. Outdoors, think drainage first

    Open-cell dry-fast foam, a mesh base, and bring them in before the first frost.

Side view of dusty blue, caramel and cream unpiped bouclé box cushions stacked on an oak benchSave
Same thickness, same soft edge, three colors: a side view that makes choosing a shade easier.

Questions people ask

What density foam is best for seat cushions?

For everyday indoor seats, high-resilience foam around 1.9–2.2 lb/ft³ (30–35 kg/m³) is a sound choice; go higher for heavy daily use or heavier sitters. Density is durability — it does not tell you how firm the foam feels.

What is the difference between foam density and firmness?

Density is weight per volume and predicts how long the foam keeps its shape. Firmness — indentation force, ILD or IFD — is how hard it feels. A dense foam can be soft and a light foam can feel firm, so ask for both.

How thick should a bench cushion be?

Most everyday benches get 3–4 in (7.5–10 cm). Next to a dining table, 2–3 in (5–7.5 cm) keeps the knees clear. Floor cushions need 4–6 in because there is no frame underneath to help.

What foam is best for outdoor cushions?

Open-cell dry-fast (reticulated) foam, which drains instead of holding water, under a UV-resistant, water-repellent fabric. Standard foam in a water-repellent cover suits a covered porch, not open weather.

Is memory foam good for bench cushions?

As a thin comfort layer on a supportive base, yes. On its own it is slow, warm and tends to bottom out on a hard bench; most seats are better with high-resilience foam.

Fair winds — Callum

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