If you have a waterproof raincoat, you could say that your coat is impermeable to the rain. Something that is impermeable does not allow water or liquid to pass through it.
Made up of the prefix im-, meaning “not,” and the adjective permeable, meaning “allowing to pass through,” impermeable is used in much the same way as impervious or impenetrable. However, more so than these words, impermeable is especially associated with liquids and is often used in a scientific or technical context. Some gadgets, like waterproof watches and underwater cameras, are designed to be impermeable.