These days, it’s unusual to find a mattress without interior springs.
There are three main kinds of modern spring units:
The open coil
The knitted spring
The pocket spring
Open Coil: Often called a ‘Bonell’ unit, these are individual springs joined with wire. On average there are between 288 and 325 springs in a 5’0 mattress.
Pocket Springs: This is the finest of the three spring systems. Each spring is housed in an individual fabric pocket. But, they manage to move independently of each other, which helps provide optimal spinal support. Spring counts vary between 800 and 5000, which should spread across two or more tiers, to provide greater comfort.