Almost all warranties cover structural defects and manufacturer errors, and most manufacturers will either repair or replace mattresses with these issues. However, it isn’t standard for warranties to cover a normal increase in the softness of the mattress material over time. Warranties also don’t typically cover normal wear and tear or accidental damage to your mattress. If your sagging is due to faulty craftsmanship, you can probably call in your warranty. However, if your mattress just softened over time, it’s doubtful your warranty will cover this issue. It never hurts to check with your manufacturer, but temper your expectations if you know your mattress is just another victim of time passage and normal use.