How should I mail a hard document through usps....?

I am sending reinstatement paperwork to a University. It contains a cover letter, a 2-page application, plus 2 additional pages (all unbound.) I don't want to stick it directly into the document mailer (which is not waterproof cause they didn't have any in the correct size.) I feel like it needs something, but what should I put the packet in? Clear folder? A simple folder? Should it be bound somehow? I want it to look professional, but not as if I were turning in a Social Studies report on Canada. Any suggestions would be appreciated. Thanks :)