Foam

for like a foam pit

Demonstration Experiment on Video
Formation of Polyurethane Foam
as well as molecular structure
http://images.search.yahoo.com/search/images/view?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dmolecular%2Bpolyurethane%2Bfoam%26ei%3DUTF-8%26fr%3Dslv8-msgr%26x%3Dwrt&w=547&h=532&imgurl=www.uni-regensburg.de%2FFakultaeten%2Fnat_Fak_IV%2FOrganische_Chemie%2FDidaktik%2FKeusch%2FGrafik%2FD-Polyurethane-e.gif&rurl=http%3A%2F%2Fwww.uni-regensburg.de%2FFakultaeten%2Fnat_Fak_IV%2FOrganische_Chemie%2FDidaktik%2FKeusch%2FD-Polyurethane-e.htm&size=7.6kB&name=D-Polyurethane-e.gif&p=molecular+polyurethane+foam&type=gif&no=1&tt=2&oid=586fc955b5079ac4&ei=UTF-8

pic of molecular structure of polyurethane foam
http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/Grafik/D-Polyurethane-e.gif

From Wikipedia, the free encyclopedia:

A polyurethane is any polymer consisting of a chain of organic units joined by ……
http://en.wikipedia.org/wiki/Polyurethane

Chemical & Engineering News: Science & Technology – Polyurethane Foam
http://pubs.acs.org/cen/whatstuff/84/8402foam.html

FLEXIBLE POLYURETHANE FOAM GLOSSARY
http://www.pfa.org/glossary.html

Polyurethane-foam
http://www.casefoam.com/Polyurethane-foam.htm

sounds like you have a cool school project going on. good luck.