Why Pull-Ups Leak: How to Tell If It’s Size or Absorbency

If your child’s pull-ups are leaking, it’s easy to jump to one conclusion: they need more absorbency.

So you size up. Or switch to overnight pull-ups. Or choose the most absorbent option you can find.

And sometimes… the leaks get worse.

Leaks are frustrating and confusing — especially when you feel like you’re already doing everything right. But here’s something most parents aren’t told early enough:

Pull-ups usually leak because of fit, not because they can’t hold enough.

Children’s continence organisations note that leaks often happen when pull-ups don’t seal properly around the legs or waist, even when absorbency is adequate [1]. 

This guide will help you work out what’s actually causing leaks, whether it’s size, absorbency, or how the two work together, and what to do next.

Quick Answer: Why Do Pull-Ups Leak?

Pull-ups usually leak because size and absorbency don’t match a child’s needs.

Leaks around the legs or waist are often caused by pull-ups being too big, which stops them sealing properly. Pull-ups that are fully soaked through are more likely an absorbency issue, especially overnight.

In most cases, leaks improve by:

• Checking fit first
• Matching absorbency to day or night use
• Avoiding unnecessary sizing up

When pull-ups fit well and have the right absorbency, leaks are far less likely.

Pull-Ups Don’t Leak for Just One Reason

Leaks aren’t a sign that pull-ups don’t work. They’re usually a sign that something isn’t matched properly.

Most leaks come down to one of three things:

1. The pull-ups don’t fit properly
2. The absorbency doesn’t match how they’re being used
3. Size and absorbency are working against each other

Once you know which one you’re dealing with, the fix is often simpler than it feels.

The Biggest Myth: “Leaks Mean We Need More Absorbency”

This is the most common assumption parents make — and it makes sense.

But absorbency only works if the pull-ups can seal properly against the body.

If pull-ups are too big, liquid can escape through leg gaps or around the waist before absorbency even has a chance to work. This is why sizing up often leads to:

• Leaks around the legs
• Pull-ups sagging when wet
• Pull-ups shifting during sleep
• Wet sheets even with overnight pull-ups

More absorbency doesn’t fix a poor fit.

Step One: Where Are the Leaks Happening?

Before changing anything, work out where the leak is coming from.

Leaks around the legs

These are usually fit-related.

• Wet pyjamas near the thighs
• Damp sheets around the legs
• Loose-looking leg openings

This often means the pull-ups are too big or not sitting snugly.

Leaks at the waist

These can be fit or absorbency-related.

• Wet waistband
• Damp clothing at the tummy or back
• Pull-ups sliding down overnight

Pull-ups soaked through

This is more likely an absorbency issue.

• Pull-ups feel heavy and fully wet
• Wetness spreads evenly through the pull-up
• Leaks happen after long wear

Step Two: Check the Fit (Not Just the Size Label)

Size labels are a guide, not a guarantee.

Two kids in the same weight range can need different fits depending on:

• Waist shape
• Thigh shape
• Height and build
• How much they move during the day or night

Pull-ups that fit well should:

• Sit snugly at the waist without digging in
• Seal comfortably around the legs
• Stay in place during movement and sleep
• Not sag when wet

Signs pull-ups are too big

• Gaps at the legs
• Sagging after wetting
• Sliding down overnight

Sizing up further usually makes leaks worse.

Signs pull-ups are too small

• Red marks on the skin
• Tight leg openings
• Complaints of discomfort

In this case, sizing up may help — but absorbency still needs to match use.

Step Three: When Absorbency Really Matters

Absorbency matters most when pull-ups are worn:

• For longer periods
• When changes aren’t possible
• Overnight

Daytime pull-ups

Day pull-ups work best when they’re:

• Lighter and less bulky
• Easy to move in
• Changed more often

Too much absorbency during the day can feel heavy or uncomfortable.

Overnight pull-ups

Overnight pull-ups need to:

• Last longer without changing
• Stay in place during sleep
• Handle heavier wetting

If leaks only happen overnight, absorbency — not size — is often the issue.

Overnight wetting is commonly linked to longer wear times and higher urine output during sleep, which is why night-time absorbency needs are often different [2]. 

Why “Just Size Up” Rarely Works

When leaks happen, many parents size up hoping it will help.

• Create leg gaps
• Reduce the seal
• Cause sagging under weight

Fit comes first. Absorbency works second.

A well-fitting pull-up with the right absorbency will usually outperform a bigger pull-up with more absorbency.

Common Leak Scenarios (and What Usually Fixes Them)

“Pull-ups leak overnight but not during the day”
→ Increase absorbency for night use
→ Keep the same size if fit is good

“Leaks started after we sized up”
→ Fit is likely too loose
→ Try the previous size with better absorbency like adding a Booster Pad

“Pull-ups feel soaked by morning”
→ Absorbency may be too low overnight

“Leaks come from the legs”
→ Fit issue
→ Check size and leg seal

Leak Diagnosis Checklist

Use this table to help work out what’s most likely causing pull-up leaks — and what to try next.

What you notice	What it usually means	What to try first
Leaks around the legs	Fit issue (pull-ups likely too big or not sealing properly)	Check size and leg fit before changing absorbency
Leaks at the waist	Fit or absorbency issue	Check waistband fit, then review absorbency
Pull-ups fully soaked through	Absorbency too low for how long they’re worn	Increase absorbency without changing size
Pull-ups sag when wet	Size may be too big	Try a better-fitting size
Leaks only overnight	Absorbency issue	Keep the same size, increase absorbency for night use
Leaks only during the day	Absorbency may be too high or fit too loose	Consider lighter absorbency or check size
Leaks started after sizing up	Fit has become too loose	Go back to the previous size with suitable absorbency
Pull-ups shift during sleep	Fit or movement issue	Check waist and leg seal before changing absorbency

When to Recheck Size and Absorbency

• Leaks start happening again
• Your child grows or changes shape
• Day and night needs change
• Sleep or drinking habits change

Child health guidance highlights that growth, routine changes, and development can affect toileting needs over time, making regular reassessment important [3]. 

Leaks aren’t failure — they’re feedback.

The Takeaway

Pull-ups leak for a reason. And most of the time, that reason isn’t obvious at first.

Understanding whether leaks are caused by size, absorbency, or the way they work together makes it much easier to fix the problem.

When pull-ups fit well and absorb what they need to, kids stay comfortable — and families get peace of mind.

Because when pull-ups work properly, kids can get on with being kids — without any fuss.

Disclaimer:
This article is intended as general information only and is based on common experiences with kids’ pull-ups. It isn’t medical advice and doesn’t replace guidance from a healthcare professional. If leaks continue despite changes to size or absorbency, or if you have concerns about your child’s health or toileting, it’s a good idea to speak with a GP, paediatrician, or other qualified health professional.