Consider the following binder:
Such binders are usually made of a single plastic sheet. The sheet is flexible and durable as you open/close the binder. I think they're formed into their U shape by a heat gun. Such binders are not to be confused with the vinyl binders that wrap a flexible vinyl around a solid thick core of wood or cardboard.
My question is: what kind of sheet this? Under this question, we may get the following sub-questions:
- If there are multiple materials that are usually used for the same purpose, what are they, and what are their pros and cons?
- What's usually the thickness of such sheets?
What I've done so far:
- This seems to say that the material is either polyethylene or polypropylene.