impermeable

im·per·me·able

adj \(ˈ)im-ˈpər-mē-ə-bəl\

Definition of IMPERMEABLE

: not permitting passage (as of a fluid) through its substance <the plasma membrane of a red blood cell is relatively impermeable to sodium and calcium ions>

—im·per·me·abil·i·ty \(ˌ)im-ˌpər-mē-ə-ˈbil-ət-ē\ noun, plural im·per·me·abil·i·ties