Cutins refer to the waxy substances that cover the outer surface of plant leaves, fruits, and stems. The antonyms for cutins can be terms like "porous," "permeable," or "penetrable." These words indicate materials that allow water and air to pass through easily. Unlike cutins, porous materials facilitate the exchange of gases and water vapor between the plant and the environment. Permeable materials, on the other hand, allow liquids and gases to pass through them. These antonyms provide a contrast to the cutins' protective qualities and describe materials that help plants exchange air and water more efficiently.