The Nike Air Max shoes uses a large air cushioning unit at the heel which is visible from the side of the midsole in most models. Different types of Air Max cushioning include "Air Max2" which does not have the "holes" in the cushioning unit and is of high pressure, "Tube Air" which is visible in several small circles on the midsole of the shoe, "Total Air" which is basically just another word for full Air Max cushioning, "Tuned Air," which is a system of individual pods supposedly "tuned" to different areas of the foot. Air in the early 1990s which was visible through the bottom of the shoe (although smaller portions of Air units are visible through the bottom of many Air Max models) and another type of Air cushioning is the low profile and very responsive "Zoom Air."