Every King Koil mattress is constructed using high-quality, resilient, high-loft upholstery materials beneath the top ticking to provide extra comfort. Even using the best components, the materials utilized for the comfort layers will naturally settle and compress due to the weight and shape of the user over time. This 'settling' or compression of less than 20 milimetres is not a structural or design defect, but a normal result from use. It will not affect the support and conformance of the mattress. Please be aware that compression of upholstery layers is not covered under this limited warranty nor should it be considered 'sagging' if you see some evidence of body impressions. To reduce body impressions, it is recommended that you rotate your mattress every 3 months (for non-TURN FREE design) to vary the areas of highest usage.