There are several things that can void an otherwise legitimate warranty claim. Here are some of the most common.
Stains are a big one. If a mattress is stained, the warranty is void. This even goes for problems in which the stain obviously didn’t cause the sag. Liquids can wear down the foams and cause them to deteriorate faster than they otherwise would. Additionally, stained mattresses are unsanitary, and no company wants to return those to the warehouse for a warranty claim. You can prevent stains to your mattress by using a waterproof mattress protector These do NOT have to feel like plastic, and they are also NOT just for the incontinent. Even just perspiration, a little bit every night over the course of 10 years, can cause a stain and wear down the foams.