LLL's BAB recommends glass containers for freezing human milk because it is the least porous
medium. Styrofoam  is full of nooks and crannies - like English muffins ;-) - and would be
extremely difficult to keep clean let alone sterilized. If glass is not available, clear hard
plastic, followed by cloudy hard plastic, are the next choices. This would especially important if
the baby concerned is premature, because of the loss of immunity factors.

Norma Ritter, IBCLC, LLLL
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"If not now, when? If not us, who?" R. Hillel