What Is it for please tell me

As far as I know, it is used usually for the handle of the gun on the pack, and sometimes other parts, if you want to make it like the movie, supposedly. But you'd have to be a pro with the stuff to actually do something like that. If you're just trying to make a prop in an easier way, check other pack plans.

Don't have time to post the info about it.. but Dr. Spengler is way off.