Here's what rhymes with impermeable.

Consider these alternatives

permeable / semipermeable overlying / lying calcareous / ideas permeability / stability absorbent / important lipopolysaccharides / rights sedimentary / century waterproof / use coralline / line basalt / called basaltic / aortic mucosal / social macromolecules / schools friable / double alluvium / antediluvian adsorbent / important erodible / notable carbonates / states uninsulated / created