Bark cells are impervious to water and gases due to the presence of a material known as Suberin. An experiment that can demonstrate this is by taking two cinnamon barks, place them into different containers, one having water and the other having nothing but just air. After sometime we observe that no swelling on shrinking occurs in the cells of the bark and the size of the bark does not changes. This proves that it is impervious to gases and water as no exchange takes place.