SYN: impermeable.
* * *
im·per·vi·ous (')im-'pər-vē-əs adj not allowing entrance or passage <medication packaged in a container \impervious to air and light>
im·per·vi·ous·ness n
* * *
im·per·vi·ous (im-purґve-əs) [L. impervius] impenetrable; not affording a passage.Medical dictionary. 2011.