Knit ADJUSTABLE FIRMNESS: Made of 40D (3.5lbs/c.ft.) high density gel-infused memory foam, Avenco 3 inch cal king bed topper can be adjusted the firmness by reversing the inner foam and provides a evenly support and maintains air flow to reduce body heat for a cooler and more restful sleeping night. Back Pain Relief: Our memory foam mattress topper california king is ergonomically designed to perfectly fit the body curves, preventing morning soreness caused by the over-sagging or hard mattresses, which is an ideal cooling gel foam mattress for side/back/stomach sleepers!