This stuff reminds me of ShapeLock (aka Friendly Plastic):

http://www.creatrope.com/blog/make/friendly-plastic-shapeloc...

http://www.lonestarairsoft.com/forums/showthread.php?t=8822

http://www.micsaund.com/2006/03/13/plastic-you-can-mold-in-y...

The differences seem to be that ShapeLock:

- requires some heat to get it in to a moldable state

- is firm, not rubbery when it sets

- is not sticky

- is reusable (just heat it up again, and you can re-shape it)

Here's something made from it:

http://www.xrobots.co.uk/android10.htm