I use several of these envelopes weekly to send books and paperwork. They are well constructed. The only change I would make would be to make the seal a little stronger. When I send books I always use packing tape on the end seals to keep them from coming open problem solved.
I perform the fulfillment function for a small house specializing in health products. We ship bottles of dietary supplements test kits and books. This versatile manila folder can handle it all. With a minimum of packing I can tape on an in-house generated postage label and it is out the door under 13 ounces first class with tracking. The clasp functions securely the flap fold is dependable and the flap gumming is excellent. It adheres well is enough to ensure adequate adhesion but not so much that it is messy. You can find a cheaper envelope but poor flap adhesion requiring taping for security? Penny wise and pound foolish says this shipper. For quality convenience versatility and dependability this is a sure winner.