---
title: "Bolster Filling: Foam or Fiber for Bolsters and Thick Backs"
url: "https://cushionguide.com/answers/bolster-thick-backrest-foam-vs-fiber-fill/"
section: "The Cutting Table"
author: "Nate Kowalski, The Pattern Engineer of Detroit"
author_url: "https://cushionguide.com/masters/nate/"
published: "2026-06-15"
updated: "2026-06-15"
keywords: "bolster filling foam or fiber, backrest cushion filling, silicone ball fill, wedge backrest foam, neck roll filling"
---

# For a bolster or a very thick backrest, should I choose foam or silicone ball fill?

*Filling is a shape decision before it's a comfort decision. The thicker and flatter the piece, the more it needs foam to hold its line.*

Also asked as: Foam filling or silicone ball filling?; What would you recommend?

> **The quick answer:** Choose foam for a non-tufted backrest 12-14 in (30-35 cm) thick, often cut as a wedge, and silicone ball fill for round arm bolsters, because silicone balls can't hold a backrest that thick. For a neck roll, the workshop recommends shredded foam, which supports without being very soft, and the filling is included in the price.

![Stacked pyramid of bolsters on a linen daybed cushion: plum velvet on top, navy corduroy, burgundy tweed and green stripe](https://cushionguide.com/media/bolster-pillows/plum-navy-burgundy-bolster-pyramid-linen-daybed-1600.webp "Bolsters sized to match the green stripe, piled into a pyramid so every end cap and fabric shows at once.")

## Key facts

- Silicone ball fill can't hold a 12-14 in (30-35 cm) non-tufted backrest.
- Thick backrests are filled with foam.
- Wedge backrest example: 12 in (30 cm) at the bottom, 8 in (20 cm) at the top.
- Silicone ball fill suits round arm bolsters.
- Neck rolls can take shredded foam or solid firm foam.
- Shredded foam is the workshop's pick for neck rolls.
- Filling is included in the price of a neck roll.

## Filling by shape, on one sheet

| Piece | Filling | Why |
|---|---|---|
| Non-tufted backrest, 12-14 in (30-35 cm) thick | Foam, often cut as a wedge | Silicone balls can't hold that shape |
| Round arm bolster | Silicone ball fill | Suits the round form |
| Neck roll | Shredded foam (recommended) or solid firm foam | Shredded is supportive, not very soft |

## The wedge backrest, dimensioned

| Measurement | Value |
|---|---|
| Thickness at the bottom edge | 12 in (30 cm) |
| Thickness at the top edge | 8 in (20 cm) |
| Taper, bottom to top | 4 in (10 cm) |

## Why loose fill suits round, and foam suits flat

Silicone ball fill is loose by design: the balls slide past each other. In a round arm bolster that works, because the cylinder of fabric is the shape. In a flat, non-tufted backrest 12-14 in (30-35 cm) thick, the balls can't hold the shape, so the workshop uses foam.

Cutting that foam as a wedge, 12 in (30 cm) at the bottom and 8 in (20 cm) at the top, tips the sitter back at an angle instead of propping them bolt upright. Angles are just lengths in disguise, partner: two thicknesses and a height define the whole piece.

Neck rolls sit in between. Shredded foam or solid firm foam both work; the workshop recommends shredded because it isn't very soft and makes a good roll. What will yours lean against, a wall or a frame?

More in [backrest cushions](https://cushionguide.com/cushions/backrest-cushions/), [shredded foam vs wedge backs](https://cushionguide.com/guides/back-cushion-fill-shredded-foam-vs-wedge/), [bolster size and diameter](https://cushionguide.com/guides/bolster-pillow-size-diameter/) and the glossary's [cluster fiber](https://cushionguide.com/glossary/#cluster-fiber).

> **Tailor's margin:** A non-tufted backrest 12-14 in thick needs foam, not silicone balls; cut it as a wedge, 12 in at the bottom and 8 in at the top.

> Silicone ball fill suits a round arm bolster; a flat backrest 12-14 in thick needs foam to hold its shape.
>
> — Nate Kowalski

## Buyer questions

**A common question:** For a very thick backrest, foam or silicone ball filling?

**The workshop's answer:** Foam. A non-tufted backrest 12-14 in (30-35 cm) thick can't hold its shape with silicone balls, so the workshop cuts foam as a wedge, for example 12 in (30 cm) deep at the bottom and 8 in (20 cm) at the top. Silicone ball fill suits the round arm bolsters.

**A common question:** Should my neck roll be shredded foam or firm foam?

**The workshop's answer:** Either works. The workshop recommended shredded foam: it isn't very soft and makes a good neck roll. The filling is included in the price.

**A common question:** Does a cushion come with the foam, or only the cover?

**The workshop's answer:** The foam is included. Standard custom cushions ship complete with a high-density foam insert in a zippered, washable cover; covers-only is a separate option with no filling.

## Questions buyers ask next

### Is silicone ball fill the same thing as fiberfill?

Close cousins. Silicone ball fill is polyester fiber rolled into small, often silicone-coated balls that slide past each other instead of matting, so it stays springy longer than plain fiberfill. That looseness is why it suits round bolsters.

### How does a wedge backrest differ from a straight one?

A wedge is thicker at the bottom than at the top, for example 12 in (30 cm) tapering to 8 in (20 cm). As a backrest it tips you back at an angle instead of sitting you upright against a flat block.

### What foam density is used, in US terms?

About 2.0 lb/ft³ (32 kg/m³), above the usual 1.8 lb high-density threshold. It is high-resilience cold foam at roughly ILD 42, though no official ILD certificate is issued.

## Related at the atelier

- [Can I buy just the foam inserts, without the covers?](https://cushionguide.com/answers/buy-foam-inserts-without-covers/): Yes, foam inserts and fillings are sold on their own, without covers.
- [Are the back cushions the same foam as the seat?](https://cushionguide.com/answers/back-cushion-filling-shredded-vs-solid-foam/): Back cushions are not the same foam as the seat: seats are firm solid foam at 32 density (32 kg/m³, about 2.0 lb/ft³), while back pillows are usually shredded foam or fiber, softer to lean on.
- [Are tufted floor cushions firm or soft?](https://cushionguide.com/answers/tufted-floor-cushion-firmness/): Tufted floor cushions are firm: the workshop rates them about 6-7 on a scale where 1 is very plush and 10 is a firm bed you barely sink into.
- [Back cushion filling compared: shredded foam, a solid wedge or fiber](https://cushionguide.com/guides/back-cushion-fill-shredded-foam-vs-wedge/): For most benches and banquettes, a shredded-foam back pillow over a firm foam seat is the right default: soft to lean on, yet it keeps its shape against a wall.
- [Replacement sofa and couch cushions: measuring, foam and covers](https://cushionguide.com/guides/replacement-sofa-seat-cushions/): To replace sofa cushions, send the length, depth and thickness of each piece, measured from the old cushion if it fit well or from the seat deck if it didn't, with photos of a tape along every side.
- [How to keep back cushions upright on benches and banquettes](https://cushionguide.com/guides/back-cushions-staying-upright/): To keep back cushions in place, match the fix to what's behind them: ties for slats or a rail, a non-slip backing for a flat wall, a wedge shape for a lean.
- [How tall should a back cushion be? Sizing backrests to your seat](https://cushionguide.com/guides/back-cushion-height-sizing/)

*± 1/4 in — Nate*

---

Written by Nate Kowalski (https://cushionguide.com/masters/nate/) for CushionGuide (https://cushionguide.com/about/). The site explains made-to-measure cushions and the partner workshop makes them; measurements are in inches first. This Markdown mirrors the page at https://cushionguide.com/answers/bolster-thick-backrest-foam-vs-fiber-fill/