'The Breastfeeding Answer Book', LLLI, Revised Edition 01/97 recommends glass
storage containers.  Second choice: clear hard plastic - polycarbonate.
 Third choice: cloudy hard plastic - polypropylene.  Lid: a solid single
piece cap. Regarding milk storage bags:  Quote: "some recommend against their
use, particularly for hospitalized babies, because there is more risk of
leakage than with hard-sided containers and they are not as airtight,
increasing the possibility of contamination (Arnold 1995).  One study
(Goldblum 1981) found a 60% decrease in some of the milk's antibodies and a
loss of fat that adhered to the plastic sides of the milk bags. However, only
the thin, plastic disposable bottle liners were studied, so these findings
may not apply to the thicker bags specially designed for freezing human milk.
 Also, these results have not been duplicated."  Page 189

Hope this helps,
Leona Simoes, LLLL