You notice a dip where you sleep and immediately wonder whether your mattress is wearing out or simply settling in. It is one of the most common mattress worries, and the answer matters, because one is normal and the other may be a warranty defect.
This guide explains the difference between body impressions and true sagging, how warranty assessors measure a dip, and what you can do about each.
What Body Impressions Are
Body impressions are slight indentations that form where you lie, as the comfort layers soften and conform to your body over time. A small amount of this is completely normal and is sometimes even a sign the comfort layers are doing their job.
Crucially, body impressions sit in the soft top layers and usually spring back when there is no weight on them. They are part of a mattress settling in, not failing.
What True Sagging Looks Like
Sagging is different. It is a permanent loss of support, where the mattress no longer returns to a flat surface and the dip remains even with no weight on it.
True sagging often means the support core or foams have broken down, leaving you unsupported and your spine out of alignment. This is the kind of dip that causes back and hip aches and signals a real problem.
How to Measure a Dip the Way an Assessor Would
Warranties typically cover sagging beyond a stated depth, measured in a specific way. You can do a rough version at home.
- Strip the bedding so you are measuring the bare mattress.
- Lay a straight edge, such as a broom handle, across the mattress over the dip.
- Measure the gap between the straight edge and the lowest point of the dip, with no weight on the bed.
- Compare that depth to the threshold stated in your warranty.
Important: every brand sets its own covered sag depth and conditions, so check your specific warranty document for the exact figure and measuring method.
Common Causes of Premature Sagging
If a mattress sags early, the cause is often one of these.
- Low-density comfort foam that compresses permanently. Our guide on foam density explains why this matters.
- An unsupportive or wrong bed base, such as slats spaced too far apart.
- Never rotating the mattress, so one area takes all the load.
Looking after the basics genuinely helps; see how to extend the life of your mattress.
What's Typically Covered vs Not
As a general pattern, warranties cover manufacturing defects, including sagging beyond the stated depth, but not normal body impressions within the allowed range, damage from an unsuitable base, or general wear. Misusing the mattress, such as flipping a one-sided model, can also void cover.
Because terms vary, always read your own warranty for what counts as a defect and what voids it.
How to Slow Impressions Forming
A few habits keep your sleeping surface even for longer.
- Rotate the mattress head-to-foot every few months.
- Use a supportive base with appropriately spaced slats.
- Avoid always sleeping in the exact same spot if the bed is larger than you need.
Frequently Asked Questions
Is it normal for a new mattress to have body impressions?
Yes, a small amount is normal as the comfort layers soften and conform to your body. As long as the surface springs back when unweighted and stays within the allowed depth, it is settling in, not failing.
How much sagging is covered under warranty?
It depends entirely on the brand, which sets its own covered depth and measuring method. Check your warranty document for the exact threshold; sagging beyond that figure is generally treated as a defect.
Why is my mattress sinking in the middle?
A persistent dip that does not spring back usually points to broken-down foam or an unsupportive base. Low-density foam, a sagging base, or never rotating the mattress are common causes. If it exceeds your warranty's sag depth, it may be a defect.
How do you measure mattress sag?
Strip the bed, lay a straight edge across the dip, and measure the gap to the lowest point with no weight on the mattress. Compare that depth to your warranty's stated threshold.
