impermeable

adjective

im·​per·​me·​able (ˌ)im-ˈpər-mē-ə-bəl 

: not permitting passage (as of a fluid) through its substance

broadly : impervious

impermeability

(ˌ)im-ˌpər-mē-ə-ˈbi-lə-tē 

noun

Synonyms

• dense
• impervious
• impenetrable
• impassable
• thick
• close
• sturdy

Examples of impermeable in a Sentence

an impermeable layer of rock

a fabric impermeable to moisture

Recent Examples on the Web

The part of Texas that flooded last week is known as Flash Flood Alley because of its impermeable limestone hills and frequent downpours, but these floods were unusually severe for the area. —Rebecca Hersher, NPR, 7 July 2025

The spongy material is mostly made of air, yet nearly impermeable to both air and liquid. —Brandee Gruener, Southern Living, 7 May 2025

Given the area’s especially hard, impermeable soil and the high cost of installing private wastewater systems, many residents have resorted to straight piping to deal with human wastewater. —Curtis Bunn, NBC news, 1 May 2025

What if the girls all band together and reject me like an impermeable cellular membrane, keeping me out, unable to penetrate their circle of friendship? —Michael Nied, People.com, 28 Apr. 2025

Word History

Etymology

Late Latin impermeabilis, from Latin in- + Late Latin permeabilis permeable

First Known Use

1661, in the meaning defined above

Rhymes for impermeable

• permeable
• semipermeable

Kids Definition

impermeable

adjective

im·​per·​me·​able (ˈ)im-ˈpər-mē-ə-bəl 

: not permitting passage (as of a fluid) through the material of which it is made

impermeability

(ˌ)im-ˌpər-mē-ə-ˈbil-ət-ē 

noun

Medical Definition

impermeable

adjective

im·​per·​me·​able (ˈ)im-ˈpər-mē-ə-bəl 

: 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

impermeability

(ˌ)im-ˌpər-mē-ə-ˈbil-ət-ē 

noun

plural impermeabilities