As the construction varies from model to model so does the warranty. Be extremely diligent to learn about the warranty of any given product. Warranties are design to protect consumer against manufacturer’s defects for certain period of time, and majority memory foam mattress warranties protect customers against excessive sagging. Excessive sagging is typically referred to as an indentation/imprint/depression greater than 1.5” for most of the mattresses, but memory foam mattress manufacturers consider indentation greater than 3/4" (some even ½”) as an excessive sagging under warranty. Most warranties start with a full mattress replacement for an initial period of time, and change to a limited (pro-rated) warranty as years go by. While comparing memory foam mattress warranties, you can find full replacement warranties for as little as 2 years and as high as 10 years, with overall warranty duration up to 25 years.