1. not allowing liquids or gases to pass through

Examples

• The raincoat is made of impermeable fabric that keeps you completely dry.
• Clay soil is relatively impermeable to water.
• The scientist tested whether the membrane was impermeable to certain gases.
• Rubber gloves provide an impermeable barrier against chemicals.
• The basement walls were sealed with an impermeable coating.
• Oil cannot penetrate the impermeable rock layer.