Having worked in a plastics plant for several years...

Although most all of the zippered bags you find from the various manufacturers
are made of bi-axially aligned poly-ethylene plastics... there are many grades
of it which will determine primarily their durability and there response to
environmental factors such as chemicals like alcohol, oils etc and secondly to
heat, cold and UV radiation.

There are many additives that can be put in the plastics to change its
durability and resilience.  That is how you have the differing grades you see
in the stores such as heavy weight. which may be multi-layered or designed for
freezer, microwave and even oven safe.

There seems to be no indication as to a problem with any of the commercially
available types.  Any problems seem to be with the quality of the assembly of
the seems and zippers and not the plastics themselves.

By the late 80's most manufacturers were purchasing the stock pellets from a
couple companies such as Kane, Quanex or Dupont and the little guys either went
away or improved, but mostly became specialist in the additives.

This said, Some of the old cheep bags will become oily after a while if left in
a warm light free place, whereas in light they may become brittle or yellow.

Leslie Allen Crnkovic




Are all brands of ziplock-style bags okay for packing shells that may be in
storage for a year or two? Are any of them?