Any material, as said used correctly.
To be a bit of a smartass...

The hardest part is to make it inescapable *without hurting the victim too much*.
Of course, you could take a rope and tie it that tight that any limbs go instantly numb, would be impossible to escape from that. But we don't want such things, do we? ,-)
Cheers
FF
There are 10 kind of people in the world.
Those who understand binary numeral system, and those who don't.