13.5 open coil bonnell spring for a longer life. Mattress is 9-10 inches deep with a top layer of memory foam. Get a grey Cool Blue memory foam mattress. Choose from six sizes (see full details and prices below). Medium - firm comfort, perfect for side or front sleepers. Hypoallergenic filling which is ideal for allergy sufferers. | Grey Cool Blue Memory Foam Mattress | Wowcher