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mattresses

Open Coil and Bonnell Spring Systems

Entity: open coil Bonnell mattress

Neat mattress with turned-down sheets on an upholstered bed in soft daylight
How a finished mattress and bedding stack can look once the bed is made.

In short

Open-coil mattresses use one linked spring grid, not separate fabric pockets. The Bonnell spring is an hourglass-shaped coil tied to its neighbours with wire. Because the coils share load through the grid, movement travels across the bed more than in pocket sprung units. Open coil beds often cost less. Partner movement is usually easier to feel.

How it works

Diagram of Bonnell hourglass coils linked by helical wires in an open-coil grid
Open-coil Bonnell units share load through a connected wire lattice.

Materials used

  • steel Bonnell or continuous coils
  • helical lacing wire
  • padding and quilt layers

Average lifespan

5– 8 years

Bonnell shape

The Bonnell coil is wider at the top and bottom and narrower in the middle. That hourglass shape gives a steady push-back feel. Spring counts are usually a few hundred, not thousands. The coils are larger than pocket springs — see spring count.

Continuous coil variants

Some open-coil units use long rows of wire instead of separate Bonnell coils. The idea is the same: one connected spring surface, not independent pockets. Brand names in this family (for example Miracoil) still sit under interconnected-spring physics — judge the full mattress stack, not the trademark alone.

Motion and roll-together

Because coils are linked together, movement travels across the unit more easily than in pocket sprung designs. That raises motion transfer and can cause roll-together on softer top layers.

Where open coil still appears

  • Guest beds and kids’ beds where cost matters
  • Some budget “hybrid” stacks with foam over open coil — check the spring type
  • Traditional builds with natural fillings

Frequently asked questions

What is an open coil mattress?
An open-coil mattress uses one linked spring grid. Coils connect to their neighbours, so load and movement travel across the surface more than in pocket sprung beds.
Is Bonnell the same as pocket sprung?
No. Bonnell coils are usually hourglass-shaped and wired together. Pocket springs sit in separate fabric pockets and move more independently. See pocket sprung vs open coil.
Who might choose open coil?
People who want a traditional spring feel and accept more partner movement transfer. Pocket sprung or hybrids usually isolate motion better.