The Cushion Atlas · Pillows, covers & foam

Foam inserts and cushion fillings, by the numbers

A cushion is a cover wrapped around a number. The number is the foam: its density, its thickness and how much bigger it was cut than its cover. Here are the numbers, tolerances included.

Atlas entry by Nate

The Pattern Engineer of Detroit · February 23, 2026 · Updated September 24, 2026

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A light press shows how the nubbly weave feels under the hand and how firmly the fill holds its edge.

The quick answer

A foam insert is the solid core inside a zippered cushion cover, and it can be bought on its own in any size. Custom seat cushions use high-density foam of about 2.0 lb/ft³ (32 kg/m³), medium-firm at roughly 6-7 on a 10-point scale. The thinnest standard insert is 2 in (5 cm); shredded foam, fiber and memory foam are the alternatives.

Shapes to choose from

Every one is cut to your measurements. The number is how many readings the atelier has published for that shape.

Sizes & measuring

Thickness and measuring, on the cutting table

The limits the workroom cuts to. Write your own numbers to the nearest 1/4 in.

Thinnest standard	2 in (5 cm)
Thinner still	1 in (2.5 cm) or 3/4 in (2 cm) only without piping; 1 1/4 in (3 cm) can take piping
Thicker builds	6, 7 and 8 in (15, 18, 20 cm), 12 in (30 cm) floor couches, and stacked layers of about 10 1/2 to 15 3/4 in (27-40 cm), at a surcharge
Fit to cover	Firm foam is cut slightly larger than its cover so the cover looks full; it takes two people to insert
Front overhang	Up to about 2 in (5 cm) past the front of a bench when an inner support wrap is added
Measuring a delivered insert	Wait 3-4 days after unpacking; then length edge to edge, width seam to seam, thickness straight up

Fabrics that work

Open a family for its swatch book, care notes and neighbors.

What a foam insert is, and when you buy one alone

Every custom cushion ships complete: a foam insert inside a removable zippered cover. You buy a foam insert on its own when the cover is fine and the core is not, or when you have covers and nothing to put in them. Buyers ask for four kinds:

Small pillow fillings, 14 x 14 in (36 x 36 cm) and 10 x 10 in (25 x 25 cm).
Foam-only L-shaped backrest inserts for floor sofas.
Full sofa foam sets: two seat mattresses and two armrest foams, plus the 4 metal supports in the photograph if you need the frame.
Replacement pieces for a single seat that stayed flat.

Sofa fillings bought alone cost less than a complete filled sofa. Covers are sold separately under custom cushion covers; the frames belong to modular floor sofas.

Odd shapes: the numbers have to close

Angles are just lengths in disguise. A trapezoid insert needs four numbers, and they have to agree before anything is cut. A real check from a past order: front 106 in (269 cm), back 56 in (142 cm), two angled sides of 35 in (89 cm).

Front minus back: 106 in minus 56 in = 50 in.
Half of that is each side's offset: 25 in.
Depth = √(35² − 25²) = √600 ≈ 24.5 in (62 cm).

If the depth does not come out of your own numbers, one of them is wrong, and it is cheaper to find out now. A drawing with every edge measured is enough; don't post a paper template, photograph it. The trapezoid cushion calculator runs the same arithmetic.

Edges follow thickness. A piped box edge works from 1 1/4 in (3 cm) up; below that, the seam goes plain.

Foam and fill, in both units

Where it goes	What it is	Density	Feel
Bench, banquette and seat cushions	High-density polyurethane, high-resilience cold foam	About 2.0 lb/ft³ (32 kg/m³)	Medium-firm, about 6-7 of 10; a flat, structured top
Floor and modular sofa seat mattresses	High-density cold foam	About 1.75 lb/ft³ (28 kg/m³); some quoted up to 32 kg/m³	Medium-hard; softens slightly with use
Throw pillows, back pillows, soft backrests	Shredded foam in its own inner cover	—	Softer than solid foam, not very soft
Thick backrests	Foam wedge in 1-3 pieces	—	Holds a 12-14 in (30-35 cm) profile that fiber cannot
On request	Silicone fiber, high-density memory foam, cotton or organic cotton, latex on some models	Varies	Fiber soft, foam firm; cotton and latex cost extra

Firmness, backrests and what the foam does to the look

Seats and backs do different jobs. By default a backrest is softer than its seat; ask, and it can be made equally firm. High-density foam gives a structured, flat top, the tailored look in most of our photographs, while shredded foam gives a pillow its plump face.

That difference shows through the cover. A crisp box edge in a linen-look weave or velvet needs a firm insert to hold its corners; a soft back pillow in bouclé is happy with shredded fill. Filling can also be supplied for outdoor sets in outdoor acrylic covers.

What do you want the seat to feel like at minute forty, partner, not minute one? The foam firmness finder asks the same question with sliders, and the seat height calculator checks what thickness does to your knees.

A real project

The corner that would not rise

A buyer in the US unpacked a vacuum-compressed floor sofa. Everything rose except one seat cushion, 78 x 39 x 6.5 in (198 x 99 x 17 cm), which stayed flat in one corner. The workshop asked for a few more days. After about a week the corner was still down, and on that side a foot sank to the floor.

Photos from several angles settled it. A replacement foam insert went out for that one cushion, in one piece, and the existing cover zips onto it. One part, swapped through the zipper.

Measured: Seat cushion 78 x 39 x 6.5 in
What it taught: Allow a few days for recovery; if one area is still flat after a week, photograph it and ask the workshop about replacement foam.

Mistakes that cost an insert

Measuring a vacuum-packed insert the day it arrives. Give it 3-4 days, then measure with the tape flat and readable.
Trying to wash the insert. Inserts are not washed; unzip the cover and wash that at 86°F (30°C).
Returning a covers-only order you meant as a full cushion. Ask for the foam, and the metal supports if needed, instead.
Asking fiber fill to hold a thick backrest. A 12-14 in (30-35 cm) profile needs a foam wedge.
Setting bare metal support bars on hardwood. Fit felt pads or fabric under them so they neither slide nor scratch.

Photographs from the workbench

Open any photograph large; each one has its own link and a Save button.

Black, gray and cream knotted stripe box cushion with a square self-piped corner on a bright white studio surface — Against pure white the black knots look almost printed, a sharper take on the monochrome stripe.

Close-up of stacked bench cushion corners in pale gray and slate blue linen-look weave with gold and wine red piping — A tight crop on the corners shows the heathered linen-look weave and piping eased neatly around the curve.

Macro of a red and cream herringbone twill stripe cushion corner with matching self piping — Up close, the herringbone twill in each stripe and the alternating red-and-cream welt are clearly visible.

Cutaway diagram of a caramel bouclé bench cushion showing gray foam core, white fiber wrap and outer cover — What sits under the bouclé: a 28-density foam core wrapped in soft fiber, as labeled in the diagram.

Three stacked box cushions in black and white zebra, white mudcloth and green tiger print fabric on a white background — Three bold prints on the same box shape, stacked to compare how each pattern handles the corners and gusset.

Straight-on view of a teal velvet box cushion with off-white piping on a white chair, showing its deep front gusset — Face-on, the gusset height and the level welt line are easy to judge, making this the best view for checking thickness.

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Seen side-on, the gusset height and double piping of each printed box cushion are easy to judge.

Three velvety box cushions stacked on white: cheetah spot on top, tiger stripe in the middle and zebra stripe below — Spots to stripes: three animal prints on identical box cushions, stacked to compare scale and contrast.

Three long box cushions stacked on white: black and white diamond print, emerald gold chevron and black mustard leaf print — Long, narrow window seat proportions in three prints, stacked to show how each pattern scales along a run.

Overhead view of a teal and olive striped box cushion corner with gray and teal knots, showing deep boxing and self piping — Seen from above the corner, the stripes on top line up with those on the side panel, and the full foam depth shows.

Hand pressing into a blue-gray bouclé box cushion with self piping on a cream storage bench, eucalyptus vase behind — A four-finger press shows the dense foam holding its edge while the looped bouclé gives under the hand.

Bench cushion foam at 2.0 lb/ft³ (32 kg/m³) holds its shape for years; floor sofa mattresses at 1.75 lb/ft³ (28 kg/m³) soften slightly with use.
Nate

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Patterns to read before you order

Four Patterns carry the rest of the arithmetic. Foam density in lb/ft³ and kg/m³ has the full conversion table. Density vs firmness explains why a dense foam can still feel soft. High-density foam vs memory foam, latex and fiber compares the alternatives, and the first 72 hours covers unpacking a compressed insert. Terms such as high-resilience foam are in the glossary.

Buyer questions

A common question
Can I buy just the foam inserts, without covers?
The workshop's answer
Yes. Fillings and foam inserts are sold on their own: small pillow fillings such as 14 x 14 in and 10 x 10 in, foam-only L-shaped backrest inserts, and full sofa foam sets with two seat mattresses and two armrest foams, plus the 4 metal supports if you need the frame. They go through a dedicated link, quoted as a set for your sizes, and cost less than a complete filled sofa.
A common question
What density is the foam in a custom bench cushion?
The workshop's answer
32 kg/m³, about 2.0 lb/ft³: high-density polyurethane, a high-resilience cold foam with a medium-firm feel. It is firmer and longer-lasting than the 28 kg/m³ foam often specified, and on a 3 in cushion it stays comfortable while holding its shape for years. Every custom cushion gets it as standard unless you ask for a softer one.
A common question
What density foam is in the floor sofa mattresses?
The workshop's answer
28-density high-density foam, 28 kg/m³, a medium-hard sponge foam that stays comfortable and lasts for years without collapsing. Some replies quote it as 28-32 density. The backrests are filled too, and replacement foam is sold on its own.
A common question
One cushion still hasn't puffed up days after unboxing. What should I do?
The workshop's answer
Give it a few more days and work the foam: take off the cover, shake, pull and pinch the filling, then refit the cover. Half-risen pieces often recover this way. If a section is still flat, dented or hard after several days while the rest has recovered, send photos from different angles. The shop treats it as faulty foam and ships a new piece with tracking; you move your cover onto it.
A common question
The insert smells of cigarette smoke even after airing. Can it be washed?
The workshop's answer
Washing the removable cover, several times if needed, clears the odor from the fabric, but the insert itself is too big for a home washing machine. When a backrest insert kept smelling of smoke after airing, the workshop sent a replacement filling for that backrest.
A common question
My cushion measures differently from what I ordered. What photos do you need?
The workshop's answer
Wait 3-4 days after unpacking, because vacuum compression temporarily shrinks foam and cover. Then send a photo of the cushion in place, plus photos with a tape measure laid flat: full length edge to edge, full width seam to seam, and thickness measured straight up. The workshop checks them against its records; ask it to confirm in writing how it will handle a workshop error or an ordering error.

Have it made

Have your foam insert made — ask Nate’s workshop

Every edge and both diagonals, to the nearest 1/4 in. If the numbers do not close, the workshop will say so on the call. — Nate

Leave your details and the workshop will call you to confirm measurements, fabric, foam and piping. No prices, dates or payment on this page: it is a request, not an order.

Fabric · Foam · Pipingwhat the workshop will confirm with you

Fabric: The cover cloth: weave, color and care code.
Foam: Firm foam is cut slightly larger than its cover so the cover looks full
Piping: 1 in (2.5 cm) or 3/4 in (2 cm) only without piping

Name

Phone Only for this request: no marketing calls or texts. Outside the US, add the country code.

Best time to call optional

What to make optional

Measurements optionalIn inches: length × depth × thickness, plus any angles or cut corners.

Notes optional

* Required. A member of the workshop team will call you to talk it through; nothing is charged and nothing is made until you have agreed on every detail with them.

We use these details only to answer this request and make your cushion: your name and contact details, the cushion details and photos you send, the page you came from and the ad or link that brought you, if any. The workshop that makes the cushions receives them. We don't sell them or share them for advertising, and we delete requests after 24 months. Privacy notice for requests.

Nothing is made or charged until you approve the details.

Want to pick the shape and add photos? Use the full quote form

Questions buyers ask next

How thin can a custom foam cushion be?

The thinnest standard foam is 2 in (5 cm). Cushions of 1 in (2.5 cm) or 3/4 in (2 cm) can be made only without piping, while 1 1/4 in (3 cm) can take piping. Tufted cushions cannot be made as thin as 1 in.

Why does new foam feel too big for its cover?

It is meant to. Firm foam is cut slightly larger than its cover so the cover looks full and the corners stay crisp, which is why fitting it takes two people. Foam-filled cushions get a protective layer instead of a separate inner cover.

Can I get memory foam or latex instead of standard foam?

Custom inserts can be silicone fiber (soft), foam (firm) or high-density memory foam. Latex is possible on some models at a large surcharge, and cotton or organic cotton fillings cost extra.

How firm is the standard seat foam on a 1-10 scale?

About 6-7. Backrests are softer than seats by default, but a backrest can be made equally firm if you ask. High-density foam gives a structured, flat look rather than a sink-in one.

Can a cushion hang over the front edge of a bench?

Yes, by up to about 2 in (5 cm), when an inner support wrap is added to the foam. Write the overhang into your order so the insert is cut and wrapped for it.

Is it cheaper to split a long backrest into sections?

Not in one real quote: four back cushions of about 18 x 21 5/8 in (45.5 x 55 cm) for a 72 in (182 cm) swing cost the same as one long backrest, foam inserts included. Separate pieces are easier to handle and to dry.

Is a pillow insert the same thing as a foam insert?

No. A pillow insert is a soft form for a throw pillow, filled with fiber, feathers or shredded foam. A foam insert is a cut block of seat foam for a bench, chair or mattress cover, sized by length, width and thickness. The workshop fills its pillows with shredded foam or fiber and cuts seat inserts from high-density foam.

How do I get a tight foam insert back into its cover?

Fold the foam, not the cover. Firm foam is cut slightly larger than its cover so the fabric looks full, and it takes two people to insert. Bend the foam lengthwise, feed one end into the far corners, then work the rest in bit by bit, with the zipper open around both corners. Never trim the foam to make it easier.

± 1/4 in — Nate

The Cutting Table

Buyers asked about foam inserts & cushion fillings

How do I get the foam back into my cushion cover?Answered by Harlan

Every answer at the Cutting Table

The Pattern Room