Thursday, November 20, 2008

What's Inside a Diaper? Project

We have some left over, fairly low quality [i.e. leaky], WalMart-brand diapers (White Cloud and Parent's Choice) in a size too small.  So I figured that it is time for...a Science Experiment!
I chose one diaper, and prepared the specimen for dissection:

After some preliminary incisions to remove some connective tissue, I was able to peel back the outer layer, revealing the inner guts of the diaper:

This flaky, dusty, papery, almost cotton-like material was laced with little beads:

Upon addition of water, I noticed two phases of absorption.  First there was a rapid, although weak absorption by the papery stuff.  This was followed by the second, stronger, slower absorption phase when the beads started taking up the water.
This two-stage method is fairly clever, and efficient in vivo.  The first step rapidly pulls the, well, "moisture" away from the, erhm, "source," decreasing the likelihood of instant leaks, while the second phase stores the "moisture" well for a longer period of time, thus allowing the source's "handlers" to sleep a little bit longer.

But just how much moisture can these things hold?
The dry weight of the absorbent part of the diaper is around 20 grams.  I added water until it just stopped absorbing:
The added weight of the absorbed water was around 600 grams (and the absorbed volume was similarly around 600 ml).  So, the diaper can hold around 30 times its weight in fluid.  (And these are the cheap diapers!)  I was pretty impressed.
Here are the beads at near-full absorbency:

We still have a bunch of these diapers left, so if there are any further experiments you'd like to see, please let me know in the comments.

And now you know What's Inside a Diaper.  Aside from the obvious, that is.


  1. What is this Blog coming to? Posts about diapers! What's next? Tips on nursing, toilet training, picking a day school?

  2. I'm going to say that that comment is rather silly. This is not just any post about diapers!!! And I'm sure if there is some way to scientifically analyze the process of picking a day school then it will show up too.
    I do hope though that we will see a modern version of the "Whats Inside a Chicken Project!"

  3. Eli, what are the significant features of one of the higher quality diapers. Inquisitive minds need to know!

  4. Jonathan/Yoni: Do you want Mommy to stop reading the blog?

    notElon: I have not dissected any of the higher quality diapers, since higher quality = higher cost. But from a cursory external examination and experimental evidence:
    a) Less leaks / better absorbency.
    b) Softer inside lining.
    c) Inside lining somehow allows absorption of poo, as well. I think those are the major points?

  5. I love the experiment! 30 times its weight is actually what you need some days. But that is what it can hold in liquid. How much can in hold in solid wet matter before exploding?

  6. Hmm, good question. First, I think I'll need to develop a "solid wet matter" substitute for testing. Maybe I'll just use mustard?

  7. Seems to me you still haven't done the most significant calculation: How much moisture is the source capable of producing at any given time?

  8. this project is really cool i did a project similar to this one but its " Which diaper Holds the most h2o"

  9. Takiyah,
    What did you find? If you have any of your results online, feel free to post a link in the comments here!