The vacuum packing bags are made from plastics designed as barrier resins.
Air, moisture, carbon dioxide etc. permeate plastics.
You'll notice for example that there are zip lock bags for food and zip
lock bags for freezer. That means the plastics are different.
Maybe a regular bag is just polyethylene, which is the worse barrier
plastic, but polyethylene sandwich with poly ethylene/vinyl alcohol is a
Correct. Different types of plastics have different permeabilities -- to
moisture *and* oxygen.
E.g., I wrap steaks in saran wrap and then "tin" foil. Steaks don't
leave the freezer very often (SWMBO isn't fond of beef) so they need
to hold up for longer periods than chicken or pork.
I do the same when shipping biscotti as they will experience temperature
and humidity changes between here and "there" (damn near everyplace is
wetter than here!) and it is imperative (for taste) that they remain
dry and crisp/crunchy -- during transit as well as when "stored" in
the recipient's home
I suspect a lot of the difference has to do with durability -- of
the bag's body as well as its "zipper". AFAICT, the (ziploc)
"Freezer" and "regular" bags are both LDPE.
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