Pocket springs vs open coil: the difference, and why it matters more than the spring count
Every sprung mattress in the UK uses one of two systems: open coil or pocket springs. They are made differently, feel different, wear differently, and the difference is bigger than anything a spring count tells you. Here is what each is and which to buy.
Open coil (Bonnell)
Hourglass-shaped springs, wired together at top and bottom so the whole unit moves as one piece. It is the old design, the one in the mattress you had as a child. It is cheap to make, light, and it lasts reasonably well if the wire is thick.
What you feel: a bouncy, connected surface. When your partner turns over, you move. When you sit on the edge, the whole side tips. The support is even across the mattress but does not follow your shape, so a side sleeper's hip sits on top rather than settling in.
What wears out: the wires connecting the springs start to creak, the springs lose height evenly, and cheap units get a lasting dip where the heaviest person sleeps.
Pocket springs
Each spring is sewn into its own fabric pocket, and the pockets are glued or stitched to each other. The springs are not wired together, so each one compresses on its own.
What you feel: a surface that follows your shape, because the springs under your hips compress more than the ones under your waist. Much less movement from your partner. A firmer, more supported edge if the unit has a rail or rod. The overall feel is quieter and more precise.
What wears out: individual springs can lose height under the heaviest point, but because there is no connecting wire, a pocket unit does not creak or develop the wave-like sag of an old open-coil mattress. Lifespan depends on wire gauge and the foam above it.
Side by side
| Open coil | Pocket springs | |
|---|---|---|
| Springs | Connected by wire | Independent, in fabric pockets |
| Follows your shape | No | Yes |
| Partner movement | Transfers across the bed | Mostly stays put |
| Noise with age | Creaks | Quiet |
| Edge | Tips unless framed | Firm with a rail or rod |
| Can be zoned | No | Yes |
| Typical count (king) | 300 to 400 large springs | 800 to 3,000 |
| Cost | Low | Low to high |
| Lifespan | 5 to 8 years | 7 to 12 depending on spec |
The count is not the point
Open-coil units have a few hundred large springs; pocket units have a thousand or more small ones. That is why counts are not comparable across the two systems, and why a "1,000-spring" mattress is only meaningful once you know it is pocket sprung. Within pocket springs, the count matters less than the wire gauge and the edge; see 1,000 vs 2,000 pocket springs.
When open coil is still the right buy
- A bunk bed or child's first bed, where the mattress is thin, light and replaced in a few years anyway.
- A very occasional guest bed where the budget is under £150.
- A caravan or boat, where weight matters.
For anything an adult sleeps on nightly, and for anything two people share, pocket springs are the right system, and the price gap has narrowed to the point where there is little reason to choose open coil.
Open coil in disguise
Some budget mattresses are sold as "sprung" or "coil sprung" without saying which. Some are described with a spring count that sounds pocket-like. If the spec does not say "pocket", assume open coil. If you can feel the springs move together when you press one corner, it is open coil.
How we do it
Every Chapter mattress uses pocket springs, stated with the count (for a king), the wire gauge, the spring height and the edge method, or, on The New Parent, a foam core with a micro-spring layer instead, because a foam core carries even less movement than pockets. Compare the chapters.
The short version
- Open coil: connected, bouncy, cheap, creaks with age.
- Pocket springs: independent, follow your shape, quiet, less movement transfer.
- Adults sleeping nightly, and couples: pocket springs.
- The count only means something once you know which system it is.
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