Spine-Lab Mattress 5 Zone 21cm Medium Firm Foam Bonnell Spring - King Single - WhiteSpine Lab Mattress 5 Zone 21cm Medium Firm Foam Bonnell Spring King Single White Sleep in comfort and awake refreshed with the Spine Lab 5 Zone Bonnell Spring Mattress. The 5 zone design of the mattress provides both pressure relief and support. The mattress has been designed using traditional bonnell spring construction finished with several layers of high density foam. The cool touch quilted cover and the breathable upper memory foam layer ensures