Most sturdy plastic folders are made from polypropylene.
Sheet capacity varies by product; common capacities include 12, 25, and 50 sheets.
Listings frequently describe durable, water-resistant or waterproof plastic construction, and reviewers often call them sturdy and long-lasting.
Yes — there are letter-size options described as holding standard 8-1/2 × 11-inch sheets.
Many folders come in a variety of colors; some include clear covers or front pockets for better visibility. Note that available colors may vary by purchase.