I need top opening cheap envelopes to put bridle numbers in for a horse show. These work great for me. They would probably be too fragile for heavy loads but for a light item they are just fine.
Staples' website describes the envelopes as "Heavily gummed flap seals securely." The envelopes I received had the type of glue that you would have to wet yourself in order for it to seal. Heavily gummed led me to believe it was self-sealing.
These envelopes are perfect for me to send catalogs to my Avon customers. They fit perfectly in them. The flap is already glued and stick on good to close. I have been buying them for years.