As a pediatrician Ive been asked about which type container to use and as a breastfeeding father I was even more interested.
What I've learned is the present recommendation is glass or hard plastic. Each glass or plastics of diffrent types can have immune components such as either white blood cells or antibodies stick to it. I cant recall off the top of my head which commponents stick to each type. This is discussed in Ruth Lawrence's text.
What I also tell moms is I feel the important thing is the baby getting breast milk.