This can be an  interesting science fair project; you can choose different hypotheses to prove.  For example:  Which diaper has the best performance?     What materials work inside the diaper to make it absorb and retain liquids?    Which diaper is the most cost effective? 

Once you choose what you want to prove, start by getting some ideas about the evolution of the product (tip: go to "History of the Diaper" link)    Most teachers like a well documented story, and it is always good to show that you are a well educated researcher and are ready for any question from the parents at the fair.  By the way, have your parents involved in the project -sometimes they can actually help!  Specially when they follow the KISS principles (keep it simple "and safe").  Just talk to your parents and let them know that you do not need to make things more complicated than they have to be, as most parents, including myself, have this involuntary tendency.  More than anything else, have fun with them!     :)

Read very carefully my F.A.Q. section to learn how you can test the performance of a diaper (the very next answer in this section).  A few dollars from each team member will allow you to get what you need, if you can have access to some free diapers. For example, from a little brother or sister, a nephew, a surviving great grandparent, great!  If you do not have access to them, you can buy diapers from your local store; a medium sized diaper is preferred because it will be more representative.  Of course you only need a few diapers of each brand, so buy the smallest count bag.  You can also try asking me for some free samples, but HEY!!... I am already giving you these good tips, please ask Pampers(*) or Huggies for free diapers, not me, and have them help you a little bit too.   :)  

(*) A P&G employee told me several months ago in a trade show that they may send samples to students working on science fair projects, I am not sure if the offer still stands.

If you decide to find out what makes a diaper absorb and retain liquids, this is also a very nice experiment to do.  You will have to separate the individual components of the diaper.  Tissue, pulp, superabsorbent, film, etc.   You will need to tear several diapers in order to collect enough material of each component (to understand more about diaper manufacturing, please follow the link: production process ).  You may need a mesh screen in order to separate the pulp fibers from acrylate powder (SAP).     Then do absorbency and retention test for each individual component (next section).    By the way, it is always very impressive to show how the SAP works.  A teaspoon of this granular powder will solidify a full glass of water; yes, you can turn the glass upside down and the liquid will not fall out.   This will be a  relatively more expensive experiment because you will need to extract the components from many diapers in order to be able to repeat the experiment several times at the fair. You will probably need a few mega packs.  Good Luck! (Didn't I tell you it was great to have your parents involved -just let them pay for the bill and they will remember your science fair experiment forever).

If you do not get an A+ grade, or you are not happy with your grade, please send me your feedback and let me know why do you think it happened.   Then I will improve this section, so that the next kid learns from your experience.  This is the same philosophy we used to apply at Absormex in our diaper factory for continued improvement of our processes.    Note:  Feedback up to this day has the following balance:   25-100's (A+), 6-95's (A), nothing below 95!!  An excellent record don't you think?  To download a document on how to measure diaper performance variables in a more professional way please click here (please note that there is a copyright protection statement): Diaper Performance. Please continue to the next answer for a simplified version adapted for the science fair enthusiasts.