Synonyms of impermeable

1 Syllable
firm, firms
2 Syllables
firmest, leak-proof, proofer, airtight, rainproof, compact, dense, firmer, sealed
3 Syllables
impervious, waterproof, watertight, appressed, fine-grained, nonporous, hermetic, compacting, padlocked
4 Syllables
imperviable, unpierceable, close-grained, impassable
5 Syllables
incompressible, water-resistant, impenetrable