This extra-firm mattress features Sertaâs new 711 Firm Individually Wrapped Coil Innerspring featuring durable, flexible wrapped coils that react individually to every contour of your body. It has a special coil gauge design that helps create a firmer feel across the entire mattress. Plus, a layer of Sertaâs Cool Twist Gel Foam provides enhanced, breathable comfort while Serta Support Foam helps create an extra-firm feel across the mattress. This Sertapedic mattress is compatible with a Serta adjustable foundation. Comfort Scale Rating = 1.