In the "Physics" chapter, you'll learn that air spaces compress as you descend in the water. This affects the small gas bubbles in neoprene, and as these bubbles compress, the neoprene becomes thinner. As a result, wetsuits provide less thermal protection as you dive deeper. Fortunately, the suit expands back to its original thickness as you ascend to the surface.

Some of the compressed gas bubbles do not return to their original size. With every dive, a small number become weak and break down. While you won't notice a change in your suit from one dive to the next, after a few hundred dives, a significant percentage of these bubbles may be damaged. At this point, the suit is considered to be "crushed," and needs to be replaced.