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Updated: 21 Apr 2022

How we test mattresses

What makes our mattress tests different? See how our reviews can reveal the mattresses that help you get a great night's sleep.
Ben Slater

We test dozens of double mattresses in our specialist test lab every year, but what do we actually do to them, and why are our tests the most rigorous around?

Why our mattress tests are different

Almost all free-to-access websites review mattresses using an individual tester and generate scores based on that individual’s preferences. Free sites also typically get mattresses free of charge directly from manufacturers or their PR representatives. 

As well as using multiple testers in a lab-based scenario, the Which? overall test score is calculated purely on the measurements and ratings supplied by the lab, meaning there is no room for unconscious bias when giving an overall rating. We also buy every double mattress we test, and do not accept free samples for any of our full lab tests, so you can have complete confidence in our recommendations.

What are Which? Best Buys and Don’t Buys? 

The double mattresses that impress the most in our lab tests become Best Buys. As of November 2019, any mattress that scores 73% or above is a Best Buy and comes with a solid overall recommendation, although you should still read our reviews to check for any factors that might impact your buying decision. 

Mattresses that score 45% or less are poor in multiple areas and we recommend you avoid them.

  • The best mattresses typically tick the most important boxes. They'll provide long-lasting support for your spine in most, if not all, sleeping positions and are also likely to be breathable and good at preventing the transfer of movement from one side of the bed to the other.
  • Don't Buy mattresses fall down in important areas – usually they're either unsupportive or struggle to stand the test of time, if not both.

How is the Which? score calculated?

The Which? overall score is a percentage. This score only takes into account the results of our tests and ignores price completely. 

This means that all mattresses are tested on exactly the same scale, so you can compare any model at any price and know how it measures up against its rivals in key areas. We test double mattresses and all mattresses are tested in the same way, regardless of the manufacturers’ claims. 

Weightings and star ratings 

A Which? test score is made up of dozens of individual tests and checks, from key factors such as body support and durability to breathability and stability.

To keep things simple, the most important scores are shown as star ratings out of five on the 'test results' page of each mattress review, so you can quickly work out whether a model is right for you.

The most important test results have a greater impact a mattress' overall score, as follows:

  • Performance (including how well it supports your body) (55%)
  • Durability (40%)
  • Ease of use (5%)

Our key testing criteria

Below are the key testing categories and how we evaluate each one.


Body support

Key question: how well will the double mattress support my back in the position I usually sleep in?

A good mattress keeps your spine in the same shape as when you’re standing up. To assess each mattress for back support, we measure the shape of a person's body at 36 different points when standing, and then when lying on their back on the mattresses.

We then measure the position of their spine when they're lying on their side, to check that no part of their body sinks too far into the mattress. A good mattress keeps your spine in line and parallel to the mattress.

As of November 2019, we also measure the spine a third time to assess how supportive each mattress if for people lying on their front.

We use people with different body types for these tests to check how suitable each mattress is for a wide range of buyers.

Our body support tests account for the largest proportion of our wider performance tests, which in turn account for 55% of a mattress' total test score.

Mattress stability

Key question: does the mattress move a lot when my partner turns on it?

A mattress that jiggles each time your partner moves in the night can disturb your sleep, so we measure whether you feel the mattress moving when a sleeping partner turns on it. 

A good mattress will be stable enough to prevent movement from transferring from one side of the bed to the other.

Our stability tests account for part of our wider performance tests, which in turn account for 55% of a mattress' total test score.

Turning on the mattress

Key question: is the mattress easy to roll over on or does it restrict my movement?

We assess how easy it is to roll over on the mattress for when you want to switch sleeping positions during the night. Some mattresses restrict your movement or, even worse, dip in the middle, meaning it requires a lot more effort to roll over.

Our mattress movement tests account for part of our wider performance tests, which in turn account for 55% of a mattress' total test score.


Key question: will the surface of the mattress become damp with sweat on a muggy night?

We use specially designed humidity chambers to measure how much moisture can pass through the layers of each mattress we test. 

Highly breathable mattresses allow lots of moisture to pass through, so even on very humid summer nights, the surface of the mattress is unlikely to become damp with sweat.

Breathability is different to how warm a mattress feels to lie on. We also test mattress insulation, but we don't factor this into a mattress' test score because some people prefer warmer mattresses, while others prefer cooler ones.

Our breathability tests account for the part of our wider performance tests, which in turn account for 55% of a mattress' total test score.


Key question: will the mattress stand the test of time?

In our tests, heavy barrels are run back and forth across each mattress thousands of times, to simulate approximately 10 years of use. 

We then examine whether the mattress gets harder or softer over time, and whether the mattress starts to sag, become less supportive or get damaged in any other way. 

A good mattresses will stay in a similar condition to when you first bought it, even after heavy use.

Our durability tests account for 40% of a mattress' total test score.

Ease of use

Key question: is the mattress easy to flip or rotate?

Pretty much every mattress either needs to be flipped from time to time or regularly rotated from head to toe in order to keep it in good condition.

And yet, mattresses can weigh upwards of 50kg and many don't come with any handles to make moving it any easier. So, as part of our mattress tests, we assess how easy each mattress is to manoeuvre.

Our ease of use tests account for 5% of a mattress' total test score.

Pick the perfect mattress with Which? reviews

Trying out a mattress in a shop gives you an idea of how comfy it is, but you need to know whether it will still give you a good night's sleep in years to come. Buy the wrong one and your comfy mattress could turn into a saggy dud. 

That's where Which? mattress reviews come in. We test memory-foam and pocket-sprung mattresses more thoroughly than anyone else. We can tell you everything you need to know about each mattress, including the niggling issues that you wouldn't otherwise discover until it was too late.

We don't test for comfort though, as this is subjective, but we do provide a brand comfort rating. This is based on Which? members who own a mattress from this brand. The comfort rating does not contribute to the overall test score, but can be used as a guide to this brand as a whole.

See all our mattress reviews.