There is also a pressure difference between the opposite sides of the establishment. The effect is mostly driven by the wind, whereby the air is pulled into the building on the high pressure windward part and is pushed out on the low pressure downwind side of the establishment (because of the pressure difference between the openings). A wind's effect on a structure creates regions that have positive pressure on the building's upwind area and a negative pressure on the downwind side. Thus, the building shape and local wind patterns are critical in making wind pressures that force airflow through its openings.