After processing over 1.15 million mattresses, I can usually tell which is which the moment I see one come off the truck. Here's how you can tell too.
The Quick Version
| Body Impressions | Sagging | |
|---|---|---|
| What it is | Comfort layers conforming to your shape | Structural failure of the support system |
| Where it appears | Where you sleep (shoulders, hips) | Center of mattress or across entire surface |
| Depth | Under 1.5 inches | Often 2+ inches, gets worse over time |
| Does it recover? | Partially, over hours | Never bounces back |
| Is it normal? | Yes — expected wear | No — something is broken |
| Warranty covered? | No (unless over 1.5") | Yes (if over 1.5") |
| Can you fix it? | Rotate mattress, add topper | Fix foundation or replace mattress |
The Simple Test
Lay a broomstick across your mattress. Measure the gap at the deepest point. Under 1.5 inches in your sleep area = body impression. Over 1.5 inches or in the center where you don't sleep = sagging.
If that answers your question, you're done. Keep reading for the details.
Body Impressions: Your Mattress Doing Its Job
This Is Normal. Expected, Even.
Body impressions are shallow indentations in your mattress's comfort layers — the soft foam or padding on top. They appear exactly where you sleep, matching your body's shape at the shoulders, hips, and lower back.
Think of it like breaking in shoes. The materials conform to your shape, creating a personalized sleep surface. I tell people: if your mattress didn't form any impressions at all, it would be too firm to be comfortable.
What body impressions look like:
- Shallow dips (under 1.5 inches) where you sleep
- Match your sleeping position — side sleepers see deeper hip/shoulder impressions
- Only affect the top comfort layers
- May partially recover during the day
- Stabilize after the first few weeks
Body impressions are NOT a defect. They won't be covered by warranty unless they exceed the depth threshold (usually 1.5 inches). They're just your mattress breaking in.
Sagging: Something Has Failed
This Is Structural Failure
Sagging is completely different. This is structural failure — the support system underneath has given out.
When a mattress sags, springs have lost tension, support foam has degraded, or the foundation beneath has collapsed. You get a crater that offers no support, usually in the center of the mattress or spanning the whole surface.
What sagging looks like:
- Deep depression (often 2+ inches)
- Appears in the center or across the mattress — not just where you sleep
- Never bounces back
- Gets progressively worse over time
- You feel like you're sinking into a hole
- Rolling toward the middle of the bed
Sagging Causes Real Problems
It throws off your spine alignment, causing back pain, neck stiffness, and poor sleep. If you're waking up with aches that go away as the day goes on, your mattress might be sagging.
How to Test Which One You Have
The String Test
- Remove all bedding, pads, and toppers
- Lay a broomstick or yardstick across the mattress, spanning the deepest dip
- Measure from the straight edge down to the lowest point
What the Measurement Means
| Depth | What It Means |
|---|---|
| Under 0.75" | Normal for any mattress |
| Under 1.5" | Normal wear — body impression |
| Over 1.5" | Likely a defect — check warranty |
| Over 2" | Definite sagging — needs action |
Location Matters Too
- Depression where you sleep = probably body impression
- Depression in the center where you don't sleep = sagging
- Depression across the whole mattress = structural failure
The Recovery Test
Get up and watch your mattress throughout the day. Body impressions may partially bounce back over several hours. True sagging never recovers.
What Causes Each Problem
Body Impressions Happen Because Of:
- Normal foam compression — unavoidable physics
- Lower-density foam — under 3 lb/ft³ memory foam shows impressions faster
- Body weight — heavier sleepers create deeper impressions
- Sleeping in the same spot — same position every night concentrates wear
Sagging Happens Because Of:
- No center support on queen/king frames — most common cause
- Broken or missing slats
- Worn out box spring
- Low-quality support foam — under 1.8 lb/ft³ breaks down fast
- Cheap coil construction — thin gauge wire loses tension
Every mattress develops body impressions eventually. Higher-density foam just takes longer.
The #1 cause of sagging I see? People put a queen or king mattress on a frame with no center support. The middle gradually collapses because there's nothing holding it up.
What Your Warranty Actually Covers
Most warranties cover sagging over 1.5 inches (or 0.75 inches for memory foam brands like Tempur-Pedic). Body impressions under that threshold? Not covered. That's considered normal wear.
To File a Warranty Claim:
- Measure with the string test — no weight on the mattress
- Take clear photos showing the measurement
- Keep your original receipt
- Make sure there are no stains (voids most warranties)
- Verify you used a proper foundation
Things That Void Warranties
- Stains (even unrelated to the sagging)
- Wrong foundation
- Removing the law tag
- Not rotating as directed
- No proof of purchase
Can You Fix It?
Body Impressions
You can't reverse them — the foam compression is permanent. But you can slow them down:
- Rotate your mattress 180° every 3-6 months
- Add a mattress topper (3+ inches) to mask the unevenness
- Switch sides with your partner occasionally
Sagging
Check your foundation first. This is fixable if the problem is under the mattress, not inside it:
- Look for broken slats
- Check for missing center support
- See if the frame is bowed
Adding center support legs or replacing damaged slats often fixes sagging immediately. If your foundation is solid and it's still sagging, the mattress itself has failed. Time for a new one.
How to Prevent Both Problems
For Body Impressions
- Buy higher-density foam — 4+ lb/ft³ memory foam, 1.8+ lb/ft³ support foam
- Rotate regularly — every 3-6 months
- Don't sleep in the exact same spot every single night
For Sagging
- Use proper foundation — queen/king beds need center support with legs to the floor
- Check slat spacing — no more than 3 inches apart
- Skip the old box spring for foam and hybrid mattresses — use a flat foundation or platform
The Bottom Line
Quick Summary
Body impressions = surface wear in the comfort layers, where you sleep, under 1.5 inches, normal and expected.
Sagging = structural failure of the support system, often in the center, over 1.5 inches, something is broken.
Before you blame your mattress, check your bed frame. Before you file a warranty claim, do the string test. And remember — shallow impressions that match your body shape aren't a problem. That's just your mattress conforming to you the way it's supposed to.
About This Guide
