impermeable

1 impossible to get through or into <the wall of security people surrounding the rock band was impermeable> Synonyms impassable (also impassible), impenetrable, impervious, impregnableRelated Words close, compact, dense, thick, tight; compressed, condensed; sturdy, substantial, tough; firm, frozen, hard, solid, stiff; inflexible, rigid, unbending, unyieldingNear Antonyms soft, squishy; bendable, elastic, flexible, giving, malleable, pliable, yielding; absorbent, porousAntonyms negotiable, passable, penetrable, permeable

2 not allowing penetration (as by gas, liquid, or light) <an impermeable seal on the ancient tomb had preserved the artifacts exceptionally well> Synonyms impenetrable, tight, imperviousRelated Words close, compact, dense, snug, thick; airtight, hermetic (also hermetical), leakproof, watertight; lightproof, soundproof, waterproofNear Antonyms absorbent, leaky, porous, unsealedAntonyms penetrable, permeable, pervious