Impermeable (adjective)

1. Not allowing liquids or gases to pass through.
2. Not allowing something to enter or be passed through; impenetrable.

Origin:

Early 19th century: from french, from in- "not" + perméable "permeable".

Examples:

1. The suit is made from an impermeable material that keeps water out.
2. The soil is impermeable and does not allow water to soak in.
3. The walls of the building are impermeable to sound.
4. The membrane is impermeable to certain molecules, making it ideal for separating different substances.
5. The coating on the metal is impermeable to rust.