When to Size Up
If you're wondering why your baby's diaper is leaking frequently, especially overnight, it's likely time to move up a size. Here's how to know for sure:
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Frequent leaks overnight or during naps - the absorbency may no longer be enough for your baby's output. Larger sizes contain more SAP (super absorbent polymer) and offer higher absorbency capacity.
- Blowouts up the back or sides - they may have outgrown the length/depth and need to size up for better coverage.
- Red marks or indentations around the waist or legs - a sign it's too snug.
- Body shape differences - not all babies carry weight the same way. A baby with chubby thighs, rounder tummy or longer torso might outgrow the fit of the diaper size sooner than a baby of the same weight with a different shape.
- Sudden growth spurts - they can come out of nowhere and mean they have outgrown the size almost overnight.
- Nearing the top of the weight range - Even if your baby is technically within the weight range on the pack, the fit might already be too small. Example: If your baby is 16 lb and you're still using Size 3 (8-18 lb), try moving to Size 4 (15-31 lb) - especially if you're seeing red marks, blowouts, or overnight leaks.
When to Size Down
Leaks can also happen if the diaper is too big to stay snug. Look out for:
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Gaps at the waist, back or thighs - the diaper isn't sealing properly. A smaller size will give a snug, secure fit that holds liquid in.
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Diaper bunches, sags or slides down - a loose diaper will bunch at the crotch and slide down when they crawl or walk.
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Tabs overlap too much - if the tabs cross over each other at the front, the diaper is too large.
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You need faster, fuss-free changes on the go.
When to Switch to Pull-Ups
As your baby grows and becomes more active, it might be time to switch from tab-style diapers to Joonya pull-up pants.
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Baby won't lie still for diaper changes.
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Leaks happen during crawling, walking for playtime.
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You're starting the potty training journey.
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You need faster, fuss-free changes on the go.
🍼 Joonya tab-style diapers are great for newborns and babies who spend most of their time lying down.
🌿Joonya pull-up pants are ideal for toddlers on the move — they flex, fit snugly, and help reduce leaks caused by shifting or sagging.
So What Size Should You Choose?
Here’s how to make sure you’re choosing the right diaper size every time:
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Follow the weight guidelines on the Joonya pack or the size guide below - they’re a great starting point.
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Size up if your baby is near the top of the weight range or you’re seeing leaks, blowouts, or tight tabs.
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Try overlapping sizes — if your baby is between weights, try the next size up and see which fits best.
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Test before you commit — before buying a bulk box, try a smaller Trial Bundle of Joonya diapers to make sure the fit is perfect for your baby.
⏳ Many parents hesitate to move up a size to avoid wasting nappies, but in reality, sizing up sooner can save you money, time, and laundry in the long run.
Pro Tips for a Leak-Free Diaper Routine
A good fit isn’t the only key to preventing leaks. Keep these tips in mind:
👉 Run a finger around the leg cuffs to make sure they’re untucked and snug
🎯 Position the diaper correctly — high enough at the back and centered in the front
⏰ Change regularly — even the best-fitting diaper can leak if it’s too full
📦 Choose a quality brand like Joonya, which offers high-performance, Danish made diapers made with non-toxic, eco-conscious materials.
The Bottom Line
Diaper leaks are frustrating — but they’re not random. In nearly every case, the wrong size is to blame. Whether it’s too tight to absorb properly or too loose to stay in place, fixing the fit is often all it takes.
So next time you’re tempted to change brands or blame the product, start with this simple check:
Is your baby in the right size diaper?
If not - don’t worry. Joonya has you covered with trial packs in all sizes, so you can find the perfect fit before committing to a bulk box.
🔄 No more guessing. No more midnight leaks.
Just a better fit - and drier nights for everyone.