Tin Tie Bags.

A bag with a flat metal strip running along the top edge. You fold the top of the bag over two or three times and press the strip flat, and it holds the fold closed.

It is one of the oldest closures in food packaging and it long predates the plastic zipper. It has survived because it reseals adequately with no moving parts, and because it looks handmade — which in speciality coffee and artisan bakery is the whole point.

Almost all tin tie bags have a kraft paper outer, because the paper and the metal strip together are what create the artisan cue.

No, and it is important not to specify one expecting that it is.

Folding the tin tie closes the bag against spillage and slows staling by restricting airflow. It does not create a hermetic seal and it does not exclude oxygen. For coffee that will be drunk within a fortnight, or bread eaten within days, that is perfectly adequate.

Where real shelf life is needed, the bag is heat sealed underneath the tin tie at filling. That seal is hermetic. The customer tears it off on first opening and uses the tin tie for every reclose after that — you get the barrier during distribution and the artisan closure in the customer's kitchen.

This is how most speciality coffee tin tie bags are actually built.

Yes, and for fresh-roasted coffee you should.

Coffee releases carbon dioxide for several days after roasting. In a bag with a heat seal under the tin tie, that gas has nowhere to go and the pack inflates — potentially splitting a seal. A one-way degassing valve lets the CO₂ out while keeping oxygen from getting in.

The valve is heat-welded into the film during manufacture, usually on the front panel. The standard speciality coffee specification is kraft outer, foil or PE liner, degassing valve, heat seal at fill, tin tie for reclose.