On 11/23/2015 6:19 AM, Frank wrote:
On 11/22/2015 11:55 AM, Don Y wrote:
There are "specialty" products that can be used to vacuum-pack
(e.g.) foodstuffs. But, AFAICT, they all use "special" media
to do so -- special bags (that you are now dependent upon
for continued use of said product).

Does anyone make a vacuum sealer that can be applied to
more generic media? Or, does the medium need special
characteristics (e.g., air channels) to be useful?

E.g., when shrink-wrapping to a "card", you draw air
*through* that card (perforations) to pull the plastic
film down onto the card (and "set" it with heat).

Could you, for example, have a device that just took regular
plastic bags (Ziploc, "baggies", etc.) and use them for this
function?

The vacuum packing bags are made from plastics designed as barrier resins.

Air, moisture, carbon dioxide etc. permeate plastics.

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

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.

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.

Maybe a regular bag is just polyethylene, which is the worse barrier plastic,
but polyethylene sandwich with poly ethylene/vinyl alcohol is a good barrier.