Dry suits retain an air space around the diver's body. Because air compresses at depth, additional air must be added to the suit to prevent the suit from squeezing the diver during descent. This is accomplished by using an inflation valve that fills the suit with air from the scuba cylinder.

The air inside a dry suit expands during ascent. If this expanding air is not vented, the diver will become more buoyant and an uncontrolled ascent results. For this reason, dry suits must have an exhaust valve to allow excess air to be vented. This valve is usually mounted on the left arm, and automatically vents air when the left arm is raised.

You should attend a dry suit specialty course if you plan to purchase or rent a dry suit. The course will teach you how to control the air space inside the suit, which is essential for your safety. You'll also learn how to take care of the dry suit, which is important for preventing failures that could result in a flooded suit.