---
title: "Open Coil (Bonnell)"
description: "What an open coil or Bonnell spring unit is, how linked springs move, and how it compares with pocket springs in UK mattresses."
url: "https://bedguide.co.uk/glossary/open-coil/"
category: "glossary"
primary_entity: "open coil"
date_published: 2026-10-21
date_modified: 2026-10-21
---

# Open Coil (Bonnell)

> An open coil mattress uses one linked grid of springs, not separate pockets. The Bonnell spring is an hourglass-shaped coil tied to its neighbours with wire. Because the coils share the load, movement travels across the bed more than in a pocket sprung unit. Open coil mattresses often cost less to make.

**Definition.** An open coil is a mattress spring unit where hourglass-shaped springs are linked by wire into one grid, so they move together.

Also called: Bonnell spring, open spring, continuous spring unit.

The linked grid spreads weight across the whole unit. That makes it feel even,
but a partner turning over is easier to feel.

Open coil mattresses often cost less than pocket sprung ones. Read the wire
gauge and the padding on top to judge the feel.

Full guide: [open coil and Bonnell spring
systems](/mattresses/open-coil-bonnell). Also: [pocket sprung vs open
coil](/compare/pocket-sprung-vs-open-coil).

---

Source: https://bedguide.co.uk/glossary/open-coil/ · BedGuide — independent UK bed guide; paid links are labelled (see /how-we-make-money/). Facts checked against official sources where possible; see https://bedguide.co.uk/editorial-policy. Report an error: https://bedguide.co.uk/corrections.