There are essentially 2 types of Spring Unit. The Bonnell or Open Coil system and the Pocket Spring system. Witnin the Briody group we use different types of bonnell spring depending on mattress quality. As a rule the Bonnell system will contain 300-400 conjoined springs of a gauge 12-13.5 (Firm-Softer). The Pocketed system will contain 1400-1800 individual springs which mould and contour as weight is applied.