Where can I find material like they use in mitter curtains in a car wash?

Question:I understand from searching the Internet that the part of a car wash that looks like long strips of fabric is called a "mitter curtain". I'd like to find this type of material to make sort of a "doggie door" on my kids' tree house where they can crawl in and out of it. Wondering where I can find a piece(s) of this stuff - wouldn't need much.

Answers:
Late night - sharp cutting tool - car wash