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How to Buy a Memory Foam Mattress That Won’t Sag in 5 Steps

So, you’re thinking about buying a memory foam mattress?

Well, if you’ve never owned or slept on one before, you may be wondering if a memory foam mattress will sag or not.

Here’s the truth:

All memory foam mattresses will sag when used often enough over a long period of time – which is also true for any type of mattress. However, some memory foam mattresses can last up to 5-7 years or more, whilst a low quality memory foam mattress could start sagging in just a few months.

And in this guide, I’m going to show you how to find a reliable memory foam mattress that won’t sag prematurely.

I’ve also included some bonus content that shows you how to stop your memory foam mattress from sagging after you’ve bought it and extend its lifespan.

Alternatively: check out my list of the best mattresses that won’t sag prematurely – which includes some high quality memory foam options.

Buy a Memory Foam Mattress that Won't Sag Infographic

How to Buy a Memory Foam Mattress that Won’t Sag

In order to find a memory foam mattress that won’t sag prematurely, it’s helpful to first understand what memory foam is, why memory foam mattress sag, the different types of mattress sagging, and how to check to see if a memory foam mattress is sagging.

The 9 Types of Mattress Sagging

A sagging memory foam mattress is one that exhibits a concave appearance when looking across the horizontal plane of the mattress surface – which is typically symptomatic of a loss of tension in the materials of the mattress, or indicative of a problem with the bed frame/sleeping surface being used.

Although you probably already know intuitively what mattress sagging is and looks like, there are actually several types of sagging that can affect memory foam mattresses, which are as follows:

  • Softening – through regular use, it’s normal for the foam in the uppermost layers of a memory foam mattress to begin to soften and compress more over time. You’re more likely to notice a change in feel if you bought a firm memory foam mattress as the materials soften and you begin to sink more into the foam.
  • Dips – a concave shape appearing in the surface of the mattress.
  • General sagging – a pronounced dip greater than 1-1.5 inches in depth will produce a visible sag in the surface of the mattress when you look across it at eye level. General sagging typically occurs in memory foam mattresses in the centre and upper half of the mattress where the most amount of weight is concentrated around the hips and shoulders.
  • Deep sagging – a very significant dip that usually indicates a serious problem with the integrity of the support core of the mattress and/or the bed frame/support surface. Sleeping on such a mattress puts you at significant risk of back pain and other types of discomfort.
  • Body impressions – it’s quite normal for permanent imprints in the surface of your memory foam mattress to appear over time in response to the foam softening where the most amount of weight is placed regularly on the mattress. These body impressions only start to affect the comfort levels when they exceed the 1-1.5″ mark and/or the support core has begun to degrade and lose tension.
  • Indentations – similar to body impressions, indentations are noticeable changes in the mattress surface that may or may not cause a variation in comfort.
  • Valleys – elongated body impressions that appear on each/one half of a double-sleeper mattress.
  • Ridges – the raised part of the mattress in between two valleys.
  • Camber (slope) – a type of sagging that takes the general form of a slope that extends from one side of the mattress to the other, caused by one heavy person sleeping on one side and a much lighter person sleeping on the other (may include valleys).

What is Memory Foam?

Memory foam is a type of polyurethane foam that’s mixed with other chemicals to give it a higher density and make it more elastic [1].

The first time I slept on a memory foam mattress, I was quite surprised at how firm it was – since I made the mistake of assuming that all memory foam mattresses were ‘soft’ because they were made of foam.

However, as I quickly found out, the feel of a memory foam mattress can change once the materials start to adapt to your body shape and weight, which made me feel uncomfortable.

But this doesn’t mean that memory foam mattresses are uncomfortable for everyone.

Memory foam can be great for side sleepers, since the adaptive nature of the foam means that it can be especially good at removing pressure from your hips and shoulders – which are common hot spots for pain in this popular sleeping position.

The Pros and Cons of Memory Foam (Mattress Makers)

Why Do Memory Foam Mattresses Sag?

Memory foam mattresses sag when the material is compressed consistently beyond its point of tolerance – which is typically around 1 inch – and eventually loses its ability to return to its original shape.

This may occur through material degradation when the memory foam is made from low density foam (less than 3 PCF) – causing the foam to lose tension and dip inwards more readily under pressure.

Whilst an improper frame/sleeping surface, excessive humidity, poor care of the mattress, or application of inappropriate cleaning strategies can also expedite the sagging of a memory foam mattress.

How Do You Check a Memory Foam Mattress For Sagging?

To check if a memory foam mattress is sagging, place a guide rod – such as a piece of wood, shower rail, or other flat object – across the length of the mattress and then use a ruler/stiff tape measure to quantify the depth of the sag.

You can move the guide rod around to identify more localised ares of sag – as demonstrated in the video below.

Weird trick to find out if your mattress is sagging (body impressions, indentations) – Natural Mattress Finder

1: Get the Right Design and Support

A good support core is critical to guarding against sagging, supporting your body properly, maintaining good posture, and keeping you comfortable.

The support capacity of a mattress is mostly influenced by the construction of the lower support layers – as opposed to the upper comfort layers (although there is some cross-over).

So the first step to finding a memory foam mattress that won’t sag is to identify the best type of design that provides sufficient support relative to your body weight and sleeping style.

There are two types of memory foam mattress designs that you can buy: all-foam and spring hybrids (latex-memory foam hybrids are also a thing, but there’s not many of them about so I’ll not discuss them any further).

As a general rule, when all other factors are equal, hybrid spring memory foam mattresses are typically less likely to sag than all-foam mattresses because their spring support core is more resilient and provides better, more adaptive support – although exceptions may arise due to differences in the material quality and exact design of the support core between brands.

Here’s an overview of each type and some guidance on picking the right option for you – along with some comments on edge support and mattress thickness.

Spring HybridAll Foam
Ave. lifespan6-10 years5-7 years
DurabilityGoodPoor – good
Sagging riskLow – fairFair – high
Body impression riskLow – fairFair – high
Ave. max weight cap.All weights<230 lbs (sometimes higher)

All-Foam

All-foam memory foam mattresses typically consist of around 3-5 inches of memory foam in the upper ‘comfort’ layers, and around 6-9 inches of high density polyfoam in the support core.

Generally speaking, all-foam memory foam mattresses are best suited to lighter and average weighted sleepers up to 230 lbs because these types of mattresses tend to sink in more which isn’t ideal for heavier weights.

However, some high quality memory foam mattress manufacturers like Amerisleep make all-foam memory foam mattresses that can support sleepers in excess of 230 lbs.

If you’re the type of sleeper that tends to shuffle around during the night then all-foam designs can make it more challenging to move around without the added bounce of the springs underneath – although this can be mitigated somewhat by going for a firmer feel and may not be as much of an issue if you’re on the lighter side.

All-foam memory foam mattresses are often favoured by couples because they are quiet and dampen movements better than spring mattresses.

An often overlooked benefit of all-foam mattresses is that they may help to guard against allergies caused by dust mites since the foam can make it harder for the critters to take up residence – although you should also look for the CertiPUR-US® certification to ensure that there are no toxic chemicals in the foam and that VOCs have been limited to guard against off gassing [2] (which can otherwise produce a chemical smell).

Spring Hybrids

Hybrid spring memory foam mattresses have a layer of memory foam in the upper comfort layer and springs in the support core.

High quality hybrid spring memory foam mattresses tend to be more durable and less likely to sag when compared to all-foam memory foam mattresses.

Look for tempered steel coils with a lower coil gauge (below 13) and a high coil count (800 – 1000+ in a queen) for enhanced durability.

If you sleep as a couple then you’ll want to go for individually wrapped pocket coils to help dampen motion transfer and inhibit noise.

Hybrid spring mattresses with a high quality memory foam top layer are great for all sleeping positions because they can provide pressure relief in the side sleeping position whilst also helping to support your spine in the front and back sleeping positions too – although the mattress firmness also plays an important part in the final comfort level (see section 3).

The spring support core is generally better at handling heavier loads over 230 lbs, whilst the added bounce can make these types of memory foam mattresses better for restless sleepers that need to switch positions more smoothly.

But again, mattress firmness can also influence the surface tension of the mattress to aid or impede mobility.

What About Thickness?

Although a thicker mattress doesn’t guarantee that your memory foam mattress won’t sag, there could be a correlation whereby a thicker mattress profile may lead to a reduction in premature sagging when all other factors are equal.

I recommend going for a mattress that’s at least 10-12 inches thick – possibly more if you’re over 230 lbs and/or you’re going for an all-foam design rather than a hybrid.

Edge Support

All-foam mattresses are notorious for sagging at the edges.

So to limit the risk of roll-off and maximise the amount of mattress surface that you can use, I recommend that you look for an all-foam mattress where the edges are reinforced with high density foam.

Or better yet, go for a hybrid memory foam mattress that has lower gauge springs around the perimeter of the mattress to combat sagging.

2: Choose Durable Foam

Not all memory foam is created equal.

Memory foam mattresses made from higher density foams tend to be more durable and longer lasing than those made with lower density memory foam.

This is because higher density memory foam is typically able to compress and return back to its original shape better than lower density memory foam can.

And whilst some high quality memory foam mattress manufacturers like Tempur-Pedic use high density foams throughout their mattresses, there are plenty of memory foam manufactures that pack their mattresses full of low density foams to reduce costs.

Going for high density memory foams is just as important as selecting the right design.

And it’s also important to note that whilst non-viscous polyfoam is often used in conjunction with memory foam to create the final mattress, the density ratings for polyfoam are different.

The table below outlines which PCF values you should look for in both memory foam and polyfoam relative to their expected durability and thus anti-sag potential:

Memory FoamPoly FoamDurability
Low density<3 PCF<1.4 – 1.5 PCFPoor
Medium density3 – 4 PCF1.5 – 1.7 PCFFair – good
High density>4 – 5 PCF>1.7 PCFGood – v. good

3: Select the Correct Firmness

The firmness of a mattress describes how hard or soft it feels when you lie down on the mattress and is set by the manufacturer using different ILD values for the foam (different to the foam density).

For example, you can buy soft, medium, and firm mattresses – with medium-soft, medium-firm, extra-soft, and extra-firm options often being available for some mattress models.

That’s right – you can actually have a ‘firm’ memory foam mattress.

Many people mistakenly think that all memory foam mattresses are soft because whilst the material may compress more deeply and conform to your body shape more closely than the upholstered layer of a spring mattress, this compression can still be achieved in a firm memory foam mattress.

You should pick the level of firmness relative to your body weight and dominant sleeping position.

Not only will this increase the chance of you being more comfortable, it can help to prevent premature sagging of your memory foam mattress because the surface tension will be better suited to your body weight and shape when it comes into contact with the surface of the mattress.

For example, sleepers over 230 lbs should generally opt for a medium-firm, firm, or extra-firm mattress to provide the extra surface tension required to keep you in good posture – which is especially important in the front sleeping position where excessive sinkage can lead to hammocking of your lower back.

Whilst softer firmnesses can allow your hips and shoulders to sink more deeply into the materials for greater pressure relief.

Picking the right mattress firmness can be difficult, but the table below can help to simplify things.

FirmnessBest Sleeping Styles
SoftSide sleepers, lighter weighted sleepers under 150 lbs, skinny sleepers looking for more pressure relief.
MediumSide, front, and back sleepers in the 130 – 230 lbs range.
FirmHeavier weighted sleepers over 230 lbs – especially front sleepers that require more hip support, or combo sleepers that need more surface tension to make switching between positions easier.

4: Use a Compatible Frame

One of the most overlooked causes of premature memory foam mattress sagging is that of using an improper frame or support surface.

For example, all-foam memory foam mattresses tend to do well on platform bases; whilst slatted frames with gaps more than 3-4 inches apart may increase the risk of sagging (and will often void the warranty) because the spaces can allow the foam base to push through and compromise the support core.

Some people even put their memory foam mattress on the floor – although I don’t recommend doing this because it can damage the mattress, increase the firmness, and void the warranty (amongst other potential problems).

The best way to ensure that your new memory foam mattress is placed on the right frame is to buy a compatible frame at the same time – most manufacturers sell suitable bases on their website and you can bundle them in at checkout (sometimes at a discount).

But if you’re just buying the mattress and you’re going to use it with your existing frame, in addition to ensuring that the structure is suitable, check the dimensions of both the frame and the mattress (mattress dimensions are usually found on the sales page) to ensure they align.

5: Get a Good Warranty and Sleep Trial

This final step is more about protecting yourself in case your new memory foam mattress begins to sag prematurely so that you can either get your money back or have the mattress/parts replaced.

So you should look for a new memory foam mattress that comes with a sleep trial that lasts at least 30 days (100 days is typical, with some manufacturers offering 1 year or more).

This will allow you to return the mattress not only if indents, dips or sags appear prematurely, but also if you just plain don’t like the mattress.

The next step is to pick a warranty that covers body impressions and sagging – the industry average covers changes in the mattress surface that start at 1.5 inches or more that don’t arise from improper use.

You’ll also want to ensure that the mattress warranty is non-prorated for at least 10 years so that you don’t have to pay for repairs/replacements (as is the case with prorated agreements).

You should also check the fine print to ensure that you don’t have to pay for shipping/returns.

Alternatively: check out the best anti-sag mattresses here, where I’ve gone ahead and picked out the mattresses with the best warranties and sleep trials (for both memory foam and non-memory foam options).

How to Stop a Memory Foam Mattress Sagging

So here’s your bonus content. 🙂

Because if you’ve gone to all that trouble to buy a memory foam mattress that has all the right qualities to guard against premature sagging, it’s no good if you then treat your new mattress in a way that puts it as risk of sagging or being damaged.

So here’s 3 ways to stop your memory foam mattress from sagging after you’ve just bought it:

1: Use a Topper

Whilst the cost of buying a mattress is usually enough to make you slam your wallet shut and shudder at the thought of spending any more money, the additional purchase of a mattress topper may actually save you more money in the long run.

Because most online mattress companies will allow you to add a topper to your order when buying your new mattress (sometimes for FREE or at a discount) and this extra layer of material could help to guard against sagging and extend the lifespan of your mattress – thus reducing the relative cost per night to sleep in your new memory foam mattress.

Just be aware that toppers come in different firmnesses – giving you the potential to alter the feel of your mattress too – so make sure that you don’t get a topper that’s too soft or firm.

Also, don’t confuse a mattress topper with a mattress protector – a protector is a thin layer that goes over the mattress to protect it from damage, whilst a topper is much thicker (although it does also protect the mattress too).

A mattress topper.
A mattress topper – (Getty via Canva)

2: Rotate the Mattress Regularly

Rotating your memory foam mattress 180 degrees every 3-6 months can help to guard against sagging, body impressions, and indentations.

This is because the surface of the mattress is then exposed to a more even load over time – rather than the same pressure points every night.

Mattress rotation is especially important if you sleep as a couple of differing weights to limit valleys and camber (sloping).

But unless you have a double sided memory foam mattress, you should NOT flip your memory foam mattress – since most have a one-sided design that means you can only sleep on one side.

3: Clean the Cover Properly

Spilling liquids and other substances on to your memory foam mattress may cause the material to degrade faster which could lead to dips and indentations appearing more readily.

This can be a good reason to use a mattress protector, topper, or at the very least, a good quality fitted sheet.

Not all memory foam mattresses have the same types of cover – most are non-removable and need to be spot cleaned very carefully.

Check out my guide to cleaning mattress covers for more detailed instructions for specific types of mattress covers.

Warning: Removing the cover of some memory foam mattresses can cause the release of fiberglass, which can harm your health and ruin your home – check out my list of the best fiberglass free mattresses to find a memory foam mattress that doesn’t contain fiberglass.

Related Questions

Here are the answers to some of the most common questions related to memory foam mattresses and sagging.

How Do You Fix a Sagging Memory Foam Mattress?

You can temporarily fix a sagging memory foam mattress by placing a sheet of plywood under the mattress to firm up the support (or place the mattress on the floor) and use a firm mattress topper to cover up any body impressions, dips, and indentations in the surface of the mattress.

Does Memory Foam Lose its Firmness?

All memory foam will lose it’s firmness through extended use over a number of years due to the natural softening of the foam – following the steps outlined in this guide can help to delay this degradation process.

Why Does My Memory Foam Mattress Sink in the Middle?

Your memory foam mattress sinks in the middle because this is where the most amount of body weight and pressure is concentrated in the bed – thus leading to softening of the foam, loss of tension, and sagging.

How Long Should a Memory Foam Mattress Last?

Most memory foam mattresses last around 5-7 years, whilst hybrid spring-memory foam mattresses could last up to 6-10 years or more – although in both cases, these figures can vary significantly depending on the brand, the foam density, the construction, the frequency of use, and how well the user cares for the mattress.

Conclusion: Design and Foam Density Are Key

Out of all of the points raised in this guide, I think that the most important aspects of choosing a memory foam mattress that won’t sag is to look at the overall design of the mattress and the densities of the foam.

More specifically, a hybrid spring memory foam mattress may outlast and resist sagging better than an all-foam memory foam mattress.

In either case, you should look for the inclusion of memory foam that has a density rating of at least 3 – 4 PCF and/or polyfoam with a rating of at least 1.5 – 1.7 PCF.

Beyond this, you should ensure that your new memory foam mattress is placed on a compatible frame, that you’re covered by a non-prorated warranty that lasts at least 10 years, and comes with a sleep trial with a length of at least 30 nights to ensure that you’re comfortable in the mattress.

Rotating your mattress every 3-6 months, using a topper and/or protector, and cleaning the mattress cover correctly may help to guard against premature material degradation, sagging, and indenting of your new memory foam mattress.

Click the button below to see the best mattresses to buy that won’t sag prematurely – with both memory foam and non-memory foam options to choose from.


Sources and References

[1] Wikipedia – Memory Foam. Accessed 29/7/20.

[2] CertiPUR-US® – Overview. Accessed 29/7/20.

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