Answer:
This is a type of mattress with upright springs incorporated inside. This is a common type of mattress today. Increasing in popularity are pocket sprung mattresses; they minimize 'roll-together' and, because the springs are independent, the springs closely follow the contour of the body for increased supporty. The best matresses have 3 layers upright/interwoven springs with small pocket springs over and a 'memory foam' top layer.