What does the 10-year warranty cover on this mattress?

It covers manufacturing defects such as sagging past the allowed depth or a broken coil in the 416-coil Bonnell core, not normal softening of the thin comfort layer, stains, or damage from an unsupported base. Keep the law tag attached, use a firm foundation, and rotate head-to-foot every 3 months. Because the comfort layer is thin, proper support and rotation matter most here.