Bonnell, Pocket Springs, Multi-Layer Systems: Understanding Spring Cores

The terms describe how the steel springs in the core are arranged and connected – classic engineering knowledge, summarised here neutrally: in a Bonnell spring unit, waisted springs are connected into a single surface by spiral wires; press on one spot and the surrounding area yields with it. In a pocket spring core, each spring sits individually in a fabric pocket and can compress independently. Multi-layer systems stack two or more levels of springs on top of each other, often with different spring gauges; zoned variants deliberately vary the firmness for the shoulder, hip and leg areas.

Scientifically, things get interesting with the question of what the design means for the body. A biomechanical review shows that sleep surfaces with zoned or adjustable elasticity achieve the best spinal alignment – better than uniformly firm or uniformly soft surfaces. Independently working springs are the classic route to this point elasticity: they allow the shoulders and pelvis to sink in locally without the middle of the body losing support. Just as honestly, it must be said: robust studies demonstrating that any particular spring type is superior on health or sleep outcomes do not yet exist.

One principle is well established: trapped heat and moisture in the bed disturb sleep. During undisturbed sleep, the microclimate under the duvet typically sits at around 32 to 34 degrees Celsius and 40 to 60 percent humidity; as heat or humid heat rises, wake phases increase while deep and REM sleep decrease. That open spring structures let air circulate is a plausible engineering argument – but independent study evidence that spring cores thereby deliver measurably better sleep than other constructions is lacking. We therefore consistently label such statements as manufacturer or engineering arguments.

The Swedish manufacturer DUX, whose beds we present in Zurich, works – by its own account – with continuous steel springs in several layers; in the Pascal system, spring cassettes in three firmness levels can be swapped for the shoulder, hip and leg zones on each side of the bed. This is the practical implementation of what the research generally supports – individually adjustable, zoned elasticity – though the product-specific details are to be understood as manufacturer information. In the showroom, you can feel the difference between the designs for yourself, lying down: the same body, three very different responses from the sleep surface.