The swap that looks close
a grey mailer is the usual substitute for Jiffy padded envelopes, and it is the wrong one. A grey mailer is opaque film without that lining. It is cheaper and it is less protection.
Packaging Suppliers lists Jiffy envelopes separately because the jobs diverge as soon as the goods are on the bench.
What the right line actually does
A Jiffy envelope is the lined bag for an item that needs cushion and does not need a carton.
Jiffy Airkraft and Arofol, in gold and white, are stocked here. The shop is an authorised Jiffy distributor.
If you have already mixed them
Substituting a mailer for a Jiffy, then posting glass or a small hard item, is the damage.
TradePro at Packaging Suppliers, for trade businesses, starts at 5% off and goes up to 10% when you spend over £1,000 a month, and it adds BACS. It does not change which Jiffy envelopes you needed.
Open Jiffy envelopes when you already know this line. Envelopes come in packs. The pack count is on the page. Packaging Suppliers will still dispatch an order placed by 3pm on the same day.