Why are my cloth nappies leaking?

The most common causes of leaks in modern cloth nappies are incorrect fit and lack of absorption. Other causes include compression leaks, delaminated or damaged PUL, or not changing frequently enough. Detergent buildup does not cause nappies to leak.

Fitting a modern cloth nappy, step by step

Cloth nappies are designed to fit snug and low, like underwear. Getting the right fit can take a little practice. Use our guide to help prevent leaks, ensure your child is comfortable, and prevent clothing and linen changes.

Extra step to prevent leaks when using pocket nappies

Leaks can occur with pocket nappies because the polyester cover can prevent the liquid getting through to the inserts tucked inside the pocket.

Skip putting the inserts into the pocket altogether, instead lay them on top. This saves you time, prevents elastics from being prematurely stretched out and will help prevent leaks.

inside of modern cloth nappy
Lay inserts on top of the cover, rather than inside of the pocket

If the inserts are microfibre, it can cause irritation against the skin, so avoid putting microfibre against the skin.

Change more frequently

Most cloth nappies (excluding night nappies) last for two hours before needing to be changed. If nappies are leaking within a two-hour timeframe consider increasing the absorbency.

Add more absorbency

If the inserts are saturated, then more absorption is needed. e.g. generally one insert will not last 3 hours.

If there isn’t enough room to add more inserts into the nappy when using a low-rise* snapped one size fits most (OSFM) nappy, undo the rise snaps and add more absorbency. The additional room created will accommodate the added absorbency.

*low rise means the nappies is made to be smaller

Absorbency and feeding habits

A child changes feeding habits significantly from birth to toddlerhood. At birth the primary source of food is liquid, therefore it is expected that they will pee and poo a lot.

As a child gets older, they are able to hold their bladder and therefore can flood a nappy, in some situations the absorbency cannot keep up with that amount of liquid.

Both situations require more absorption. See Adding Absorbency for options.

Compression leaks

When inserts are saturated and are compressed (squished) it often causes the liquid to seep out, this happens often with microfiber because it works like a sponge, but also happens with bamboo, cotton and hemp.

Image comparing microfibre to bamboo

Leaks can happen when inserts are new

New cotton, hemp and bamboo inserts absorb (in total capacity) less than older ones.

The reason for this is that the fabric goes from being smooth when new, to rough over time after being washed. What happens is the surface area of the fibres increases over time with washing (friction), the fibres become looser and micro piling occurs. The greater the surface area, the more micro piling, the more absorbency.

Cotton, hemp and bamboo will continue building absorbency with use. Changing the nappy more frequently during this time will help prevent leaks. See New Nappies for more info.

With new bamboo, cotton or hemp inserts, use the bamboo/hemp/cotton side up against the skin, instead of the stay-dry layer (which is usually suede cloth/ polyester).

Image of silk fibres before and after washing
A range of different fibres under an electron microscope

Delaminated covers

Leaks can occur when a nappy cover is delaminated. What happens is the plastic layer which is water-resistant comes away from the polyester layer of the nappy cover and can be ripped.

Urine output in children

Newborn babies have very small bladders, about 20-30mls, or just bigger than a metric tablespoon.1,2,5 Children’s bladders get steadily bigger as they age, with a shift in how fast the bladder grows around age two.  Girls have bigger bladders than boys.2

How babies pee also differs among children of different ages.  Neonates urinate more often and at a higher pressure than older children.3,4 

This pattern of when children urinate guides what absorbency is needed in reusable nappies. 

Newborns need very small nappies (both because the child is small and because urine volumes are small) but the child will need changing frequently.  This is also due to when the child will poo as well as how much and how often they pee.   Many newborns poo before, during and after feeds.  Typically newborns outwet nappies before they outgrow them, and more absorbency needs to be added to nappies or they will leak. 

As children get older, their bladder capacity increases, and the amount they can pee increases, children require nappies with more absorbency.  This peaks at about six months of age, which is the largest a child is when all of their nutrition is in liquid form.

After around age two, children develop the ability to “flood” nappies, when they are dry for long periods of time (2-3 hours) and then can let go of a very large volume of urine all at once.  Almost all OSFM nappies will require boosting for toddlers if a nappy is to last 2-3 hours.

References and further reading

  1. Bachelard M, Sillen U, Hansson S, Hermansson G, Jodal U, Jacobsson B, Urodynamic pattern in asymptomatic infants: siblings of children with vesicoureteral reflux. J Urol 1999 162: 1733–1738.
  2. Kaefer-M et al, Estimating normal bladder capacity in children. J Urol. 1997 Dec;158(6):2261-4 <https://www.jurology.com/article/S0022-5347(01)68230-2/fulltext>.
  3. Sillen U, Bladder function in infants. Scand J Urol Nephrol Suppl 2004 215:69–74.
  4. Hjalmas K, Urodynamics in normal infants and children. Scand J Urol Nephrol Suppl 1988 114:20–27.
  5. Wen JG, Tong EC, Cystometry in infants and children with no apparent voiding symptoms. Br J Urol 1998 81:468–473.