How we test disposable nappies and nappy pants

Our independent reviews combine results from expert lab tests with unique insights from parents to reveal the best disposable nappies and nappy pants for your baby.

Our test results will tell you which absorb liquid quickly and lock moisture into the core away from your baby's delicate bottom.

What are Which? Best Buy, Don't Buy and Great Value nappies and nappy pants?

Best Buys

A Best Buy disposable nappy or nappy pant must excel in our tests and score 80% or above. But it's still worth reading our Best Buy reviews to check if there are any factors that might change your mind on particular ones.

Find out which disposable nappies and nappy pants you can rely on in our guide to the best disposable nappies and nappy pants.

Don't Buys

Any disposable nappy or nappy pant scoring 45% or less is a Don't Buy. This means the nappy did so poorly in our tests that we don’t recommend you buy it.

Great Value nappies

The cost of buying nappies can significantly rack up over time, which is why we've also made Great Value recommendations. These nappies or nappy pants score 65% or more in our tests and, per nappy, are at least 20% cheaper than the average cost of a nappy.

Some of our Great Value nappies also get a high enough score to be Best Buys. Read our nappy reviews and use the Best Buy and Great Value filters to find the the top nappies for your baby.

Which nappies or nappy pants absorb liquid quickest?

A nappy that soaks up liquid quickly can help reduce the number of nappy accidents you'll need to deal with.

We apply synthetic urine to the nappy and time how long it takes to fully absorb the fluid. We repeat this four times to measure the rate of absorption as the nappy fills up, which is designed to reflect a nappy being worn overnight.

A good nappy should be able to absorb wetness quickly, regardless of whether it's the first or the fourth time they wee.

Which nappies or nappy pants lock in wetness away from my baby’s skin?

To check if the nappy can keep liquid locked away inside its core, we place filter paper on top of a fully fluid-loaded nappy and weigh it down. We measure the amount of liquid absorbed by the filter paper to work out how well the nappy holds in fluid.

This is designed to replicate your baby sitting on top of a nappy that they've been wearing for a while.  

Some babies, especially those with delicate skin, can develop nappy rash if they're left in a nappy that lets wetness back onto the skin. The best nappies don't let this happen.

Which nappies or nappy pants won't leak?

Even if a nappy can soak up a lot of liquid, if it lets wetness leak through to the outside, you could end up with soggy babygrows and damp bedsheets.

We apply synthetic urine to the nappy four times, recording the amount of liquid, if any, that leaks out of the nappy each time.

Which nappies or nappy pants do parents rate?

Since September 2023, we've used a panel of 30 babies to try out each of the nappies, and got their parents to give us their thoughts and ratings for them. They cover off similar areas to our lab tests, but this time with the benefit of parent and baby experience.

Any nappies tested before September 2023 won't be comparable to ones tested after this point.

Should I buy it? 

The results from each of the tests described above, as well as the results of our survey, are combined to give an overall percentage score for each disposable nappy or nappy pant we review.

Our total test score for nappies is made up of the following factors:

50% performance lab tests

• 15% absorption rate
• 15% protection against leakage
• 15% holding wetness inside
• 5% breathability

50% user trial tests

• 15% day and night absorption
• 7.5% leakage
• 5% breathability
• 5% redness/irritation
• 5% ease of putting on and taking off
• 5% nappy fit
• 2.5% visual aspect
• 5% overall rating

Are reusable nappies worth it? Find out more about the different types and the pros and cons of using them.