I had a project like this a year ago but I didn't really score all that well.
The best results in my class were from from 'piepschuim' donno what the name is in english, foam perhaps?
Anyways, we had to keep boiling water as hot as possible for 15 minutes and
extremely tight packed foam was the best with 94 degree after 15 minutes.
If you cover it up good and wrap it around all kinda foils and stuff you could use just use a teacan, which is what I did, but apparently those things aren't as good as tight packed foam.
If your teacher is handing out rewards for originality go for straw and salt, works crap but some geek in my class still got a better note than me >_<".
this is the "foam" I am talking about
http://www.mistymountains.nl/materialen/schuim.jpg