What is a antonym for permeable

Impermeable

Watertight

Explanation:

The definition of permeable is: allowing liquids or gases to pass through it.

The opposite of this would be not allowing liquids or gases to pass through it.

This would be impermeable.

Or it could be watertight.

The definition of watertight is this: closely sealed, fastened, or fitted so that no water enters or passes through.

Answer: watertight