Common closures include hook-and-loop (Velcro), elastic band wraps, metal or plastic clasps, gummed flaps, and other easy-close styles—varies by model.
Yes—several listings are 3-hole punched so the envelope inserts directly into a standard 3-ring binder and fits like a regular binder sheet.
Most are made of plastic and are described as sturdy or protective, with some listings noting scratch-, water-, and tear-resistance. One listing in the set is a paper #10 window envelope (not plastic) meant for mailing rather than heavy-duty protection.
Options include assorted packs and single-color choices in bright hues (red, blue, purple, green, orange, yellow). Many plastic envelopes are translucent or semi-transparent so contents remain partially visible.
They hold standard and larger sheets (essays, forms, presentations), photos and letters, and small office supplies such as pens, pencils, and erasers—basically papers and small stationery items for storage or transport.