Myar Bags vs Kilner Jars For Dry Food Storage.

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With the jars being glass, they last as long as they don't break.
It depends on which closures you have SD. The clip top jars like this http://www.kilnerjarsuk.co.uk/kilnerrang...tops-round can be used quite a few times, I've got some 5 years old and the gaskets still form a seal I just pop them into hot water and it seems to work.
Jars with a screw top like this http://www.kilnerjarsuk.co.uk/kilnerrange/screwtop I don't really know, I've only been using these jars for a few years, I have re-used them but just a couple of times so can't really comment on their longevity. This is only my personal opinion, if you want to use fresh discs and gaskets that's fine.
If using Kilner jars for canning or bottling, never re-use the sealing discs or gaskets.