3
closed
3
heavy(adjective, hard, solid, rigid)
3
inaccessible(unaffected, unyielding, unbending, resistant, impervious)
3
pressure-tight(adjective, tight, proof, impervious, hermetic)
3
rainproof(adjective, resistant, impervious, watertight, waterproof)
3
solid(adjective, close, set, hard, tough)
3
substantial(adjective, close, set, hard, tough)
3
unpassable
2
air-tight(adjective, tight, proof, impervious, hermetic)
2
anesthetic
2
compacted(adjective, solid, dense, compressed)
2
compressed(adjective, set, hard, tough, firm)
2
concentrated(adjective, set, hard, tough, firm)
2
condensed(adjective, set, hard, tough, firm)
2
congested(adjective, close, solid, short, substantial)
2
consolidated(adjective, close, solid, short, substantial)
2
constipated(adjective, density)
2
crowded(adjective, close, solid, short, substantial)
2
imperforate
2
imporous(closure, density)
11 years ago|4.5k views|share |citing 
APASmart Define. (2015). impermeable thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/impermeable/thesaurus/synonyms
ChicagoSmart Define. 2015. "impermeable thesaurus" https://smartdefine.org/impermeable/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, impermeable thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/impermeable/thesaurus/synonyms>.
MLASmart Define. "impermeable thesaurus" 14 April 2015. Web. 22 September 2026. <https://smartdefine.org/impermeable/thesaurus/synonyms>