Authorised Jiffy stock is the lined bag. A grey mailer is not a short-dated substitute. This page stays with grey mailing bags, next to plain envelopes.
Packaging Suppliers keeps Mailing bags apart from a padded envelope. They are also called shoe bags. The category says they are European made from recycled film and 100% recyclable, and opaque so the contents are not visible.
What this collects
Grey mailing bags are the opaque outer for soft goods.
plain envelopes is the neighbour on this list. Plain and window envelopes are for paper that can go as a letter, not for a parcel. It is still a different range from grey mailing bags.
Before the order goes in
Choose the mailer that fits the goods. A much larger bag folds and looks like a different pack.
On Packaging Suppliers, put Mailing bags on the order with the lines it belongs to, so you are not paying a second delivery for the piece you forgot. Free UK delivery starts over £50 ex VAT.