In one embodiment, barrier coating 32 is a polymer that does not dissolve in water at temperatures above 50??? C. Suitable polymers can be selected from cellulose derivatives in which the degree of substitution is sufficient to prevent solubility above 50??? C. such as, for example, cellulose acetate lactate, cellulose lactate, methylhydroxybutyl cellulose, hydrophobically modified cellulose deriv