Mattress Sagging – Is It Time To Chuck It?

Understanding the difference between normal settlement and actual mattress sagging is usually the first step. There is a lot of confusion regarding mattress types, foam materials, and how the body rests on a surface. I want to walk you through exactly what is happening inside your bed, how to spot premature sagging, and realistic ways you might try to fix a sagging mattress (though I will be honest about the limitations).

Sagging vs. body impressions

First, let’s clear up a misconception. If your mattress starts to show a dip where you sleep, it is not necessarily defective. Most mattresses contain comfort layers (the top layers) made of foam. When you sleep in the same position every night, the weight of your body compounds on the foam materials. The air cells in the foam break down slightly, and the material settles.

This is called a "body impression." It is actually a sign that the mattress is conforming to your body weight.

Mattress sagging is different. Sagging occurs when the support core (the springs or dense polyfoam base) fails, or the comfort layers lose so much rebound that they offer no pressure relief.

If you are rolling into the middle of the bed against your will, or if you feel like you are sleeping in a hammock, you have a sagging mattress. This lack of proper support often leads to poor sleep, hip pain, and a general decline in sleep quality.

Why do mattresses sag?

To understand why a mattress is sagging, you have to look at mattress construction.

1. Natural wear and tear: Even the best mattress won't last forever. Over time, steel springs lose their tension (though this takes a long time), and foams oxidise and soften. Old mattress models usually show significant sagging after 8 to 10 years.

2. The bed base: This is huge. Often, people blame the mattress, but the issue lies with the bed frame or innerspring base. If you put a heavy hybrid mattress on a bed frame with slats spaced too far apart, the mattress will push through the gaps. The mattress follows the shape of what sits underneath it. If the bed base is made of flexible plywood, the heavy mattress will bend to the shape of the base. This is why we recommend solid timber slats that can hold a lot of weight.

3. Foam density: Low-density foams in the top layers will flatten quickly. We see premature sagging often in "bed-in-a-box" brands that use soft, low-density memory foams that make it easier to compress the mattress.

4. Uneven weight distribution: If you share a bed, chances are one partner is heavier. This creates uneven weight distribution, causing one side to wear faster than the other.

Can you fix a sagging mattress?

I will save you some reading time: rarely.

If the mattress is sagging because the internal springs have broken or the extensive foam materials have collapsed, you cannot fix it. The structure is gone.

However, I know a new mattress is a big expense. There are a few things you can try to squeeze a little more life out of an old mattress before dragging it to the council cleanup.

The plywood trick

If you suspect your bed frame or box spring is the issue, try placing a sheet of plywood between the mattress and the base. This provides a rigid, flat surface. If the sagging was caused by flexibility in the base, this might offer additional support. It won't fix the mattress itself, but it stops it from dipping further through the slats.

Rotating the mattress

You should rotate your mattress monthly for the first six months, and then every season after that. This ensures even wear. If you have a sagging area on one side, rotating it might move that dip to where your feet go (depending on the size of the sagging area). It’s not a perfect fix, but it can help with pressure relief for a while.

Using extra pillows

Some people suggest putting extra pillows or a small pillow under the sagging spot beneath the mattress. This lifts the depressed area. I see this as a very temporary fix. It usually makes the bed feel lumpy and creates uneven weight distribution. It might get you through a few nights, but it certainly won't provide quality sleep.

Will a mattress topper fix my woes

I get asked constantly if a mattress topper will fix a sagging mattress.

The honest answer is no.

A mattress topper is designed to add softness or comfort to a specific firm mattress. It contours to the surface beneath it. If your mattress is sagging, the topper will simply follow the curve of the simple sag. You will end up with a softer hole.

Buying a mattress topper for a saggy mattress is throwing good money after bad. Thicker toppers might bridge the gap slightly, but they don't provide support. They just add more material for your body to sink into.

Prevention

If you buy a new bed, you want to prevent this from happening again. You cannot stop wear and tear completely—every mattress has a lifespan—but you can stop premature breakdown.

1. Check your base: Ensure your bed frame has slats no more than 7cm apart. If you use a box spring, make sure it isn't 20 years old. A broken box spring kills a mattress.

2. Rotate: As I mentioned, rotate the mattress monthly initially.

3. Use a mattress protector: This keeps moisture out of the unnecessary comfort layers. It stops sweat from breaking down the foams and glues inside the mattress.

4. Avoid direct sunlight: If you ever strip the bed to air it out, avoid leaving the foam core in direct sunlight. UV rays oxidise foam, making it brittle. Brittle foam crumbles and leads to sagging.

5. Don't sit on the edge: Sitting in the same spot on the edge of the bed occasionally to put on shoes is fine. Doing it for hours every day will break down the side support and cause the mattress to deform.

Signs your mattress is dead

Sometimes, you have to accept reality. You need a new mattress. Here are the signs that fixing it is off the table:

• You wake up in pain: If you wake up with back stiffness that goes away an hour after you get out of bed, your mattress is failing to support your sleeping position.

• The Valley: You roll towards the middle of the bed involuntary.

• Noise: If you hear creaking or crunching, the springs are broken. Foam can't fix broken steel.

• Visible sagging: If you look at the mattress from the side and see a visible dip without anyone lying on it, the comfort layers and support core are finished.

• Age: If the old mattress is over 8-10 years old, it has done its job. Materials degrade.

Choosing the right mattress to avoid sagging

In the core

It's all about bodyweight-matched springs. The most important part of a mattress is the spring system. The spring tension must be matched to your body weight. 

On the top

You need to look at the quality of materials and construction.

Marketing terms mean nothing. "Ortho-grade," "cloudcell" - these words are usually meaningless. I have a rant about that in this article.

Memory foam can be great, but cheap memory foam (low density) will sag quickly. High-density foams (50kg/m3 and up) resist sagging much longer. High-quality natural latex is the best material for the comfort layer. It last 3-4x longer than polyurethane, and is breathable and comfortable.

Hybrid mattresses are popular because they combine springs and foam. However, ensure the foam layers on top are high quality. If the manufacturer uses 5cm of cheap foam on top of good springs, you will still get a body impression that feels like a sag.

In my factory, I prefer modular designs. This allows you to unzip the cover and replace components. If the comfort layers soften after five years, you don't have to throw the whole mattress away. You just replace the top layer of foam. It makes more sense than buying a whole new bed.

Side sleepers vs back sleepers

Sagging affects people differently based on body weight and sleeping position.

Side sleepers put a lot of pressure on their hips and shoulders. These are high-pressure points. If the mattress sags, the hips drop too low, causing the spine to curve sideways. This is a recipe for waking up with a sore lower back.

Back sleepers need their hips to be supported to maintain the natural curve of the lower spine. A saggy mattress causes the "hammock effect," rounding the back and straining ligaments.

Heavier people will wear out a mattress faster. If you are heavy, you need to look for higher-density foams and stronger spring gauges to prevent premature sagging. Standard mattress types might not provide the extra support required over the long term.

Why new mattresses fail too

You might be thinking, "Karl, I just bought this bed two years ago."

I hear this frequently. Modern manufacturing has shifted towards "one-sided" mattresses. You can't flip them, only rotate them. They rely heavily on thick pillow tops.

The problem is that many manufacturers use low-density quilting foam in that pillow top. It feels amazing in the showroom with a nice sales pitch. But after 600 nights of sleeping in the same spot, that air-filled foam flattens.

The springs underneath might be fine. But if you have a 40mm dip in the top foam, the mattress feels like it is sagging. Technically, the warranty might not cover it because they call it "normal settling," but to you, it feels like a broken bed.

This is why understanding mattress construction is key.

Final thoughts

If you are currently sleeping on a sagging mattress, check your warranty. Mattress warranty terms vary, but usually, a sag deeper than 30mm-40mm is considered a defect. You will need to measure the depth of the impression.

If you are out of warranty, try the bed frame check. Look at your slats. Put the mattress on the floor for a night to see if it feels better. If it does, buy a new base, not a new mattress.

Don't rely on a mattress topper to save a dead bed. A topper is for comfort, not support.

If you must keep the mattress for a while longer due to budget, try placing a firm board between the mattress and box spring under the sagging area, but know this is a patch, not a cure.

Eventually, for your health and sleep, you will need to invest in the best mattress option that uses high-density materials. Look for transparency from the seller. If they won't tell you the density of the foam, walk away.

You spend a third of your life in bed. Don't spend it fighting against gravity in a collapsing pit.