Why Big Babies Leak, Part 1

Little tykes have it all. They get to be carried around, cuddled, can take stuffies anywhere, and can fit into off-the-rack baby clothes. They even have physics on their side: Babies are physically less apt to leak. They benefit from surface area, curvature, and shear scale. The unfairness of physics is enough to make an adult baby cry.

To start with, babies have the advantage of surface area. Consider a baby cube. Let's say its a girl cube, one baby cube tall. Each of her six square sides will have a surface area equal to her width times her height. 6x1x1=6. Her diaper will cover some of this surface area. The baby cube will have a volume equal to her width times her height times her depth. 1x1x1=1. Some fraction of this volume would be bladder. The rest of her body will be generating waste to go through the bladder. The baby cube will also be able to be changed in public, but I digress.

In contrast to the baby cube, we have an adult baby cube. (The mathematics would apply equally to a diaper lover cube.) Let's say that the adult baby cube was two baby cubes tall. Each of his six sides would have a surface area equal to his height times his width. 6x2x2=24. That is, it has four times as much surface area as the baby cube. In turn, his volume would be equal to his height cubed. 2x2x2=8. That is, he has eight times are much volume as she does.

Since the adult baby cube has eight times as much volume, he would generate about eight times as much urine. Unfortunately for him, he only has four times as much surface area to wrap a diaper around. Every square inch of diaper has twice as much pee to soak up.

Any urine that isn't instantly absorbed by the diaper runs down towards the leg or waist gathers. Some will be absorbed before it hits the gathers. The rest runs up against the gathers at the legs or waist. Here again, physics favors babies, as part two - curvature will show. It just isn't fair.

Take care

~BitterGrey

Last Update:20 March 2011  First:20 Sept 2006   Email BitterGrey   

Do you have Questions, Tips, Suggestions, or other feedback?

Kovu asks Do you know if there are adult diapers with two tapes (one on each side that is)?

There are few. Some places still list two-tape diapers, such as They arent truly practical for adults, so most places will only carry four or six-tape diapers. However, there are still the odd exceptions. One is Safe Comfort, that still lists SureCare diapers on their website. SureCare used to be made by a division of Tyco (according to the bag I found at a thrift store one day). Independent thrift stores are usually good places to find less-than-current diapers. According to GhostWulf, diapers with only two tapes have shown up at Sams club, but these might not have been the classic wingfold design.

LilJennie adds AB Universe.com sells two types of diapers, "Cushies" and "Super Dry Kids," that have one tape per side. I have tried the Super Dry Kids diapers, and the tape isn't like a typical diaper tape -- it's wider than it is long, basically like what you'd get if you took a two-tape-per-side diaper and bridged the gap between the tapes with more tape. They seem to have solved the problem that one-tape (per side) diapers pose for adult-size babies. And they've solved it in spades. Not only is there adhesive at both the top and bottom of each side, but it's really strong. This makes sense, because the adhesive force of a piece of tape increases with surface area, and instead of one small tape at the top and another at the bottom, they've got everything in between as well.

Not only is it difficult for these tapes to come loose accidentally, it's difficult to pull them loose deliberately. The only real problem they pose is in fitting -- you must get a diaper of the correct size for you, or you won't be able to get the entire extra-wide tape on the taping panel, where it adheres best and where it can be removed without tearing the outer plastic liner. And of course then there's the fact that the rest of the diaper isn't apparently designed all that well, because they always leak for me. Great look, excellent taping system, but wear something over them if you're going to wet them.

	Related Topics: A New Yorker article on how disposable diapers are getting "Smaller"