What type of plastic is this?

I've recently noticed a lot of materials being made of this particular
translucent plastic. I believe it is called polypropylene plastic. All
the hard plastic document portfolios at office supply stores are made
of it. Here are some examples of it:

http://www.yuanpengchina.com/PP%20Box%20without%20printing.htm
http://www.yuanpengchina.com/PP%20Box%20with%20printing.htm
http://www.staples.co.uk/ENG/images/products/uk_354651_1_std.jpg

I'm find this material interesting because two pieces of it can be
attached to each other by punching a "rivet" into the plastic (instead
of say, using a metal or other material "rivet" to attach them
together). But I know nothing of the material, the process of
attaching the pieces together or whether they are within the
"consumer" realm for arts and crafts purposes.

Can anyone shed some knowledge?