It's polyester, which I found measured around 138 MPa for the thin film: http://www.shimadzu.com/an/industry/petrochemicalchemical/i206.html
That's the same as for cast iron, or bone.

Quite strong if made without nicks (takes practice). Most importantly it's hot-shrinkable. So you can make very tight joints with it (i.e. for the shelter building). See some proof (and another DIY tool guide) here (in Russian, but you can just turn off the sound for clarity, oh, he's made English subtitles already):


and here