Close-up of a section of a pneumatic de-ice boot on the leading edge of an aircraft's wing. The boot is made of reinforced rubber and the lines on the boot are rows of stitches; the strips between the stitching inflate and become half-cylindrical, thus breaking ice off the wing leading edge. When not in use the strips are held flat by vacuum air; the airflow is changed to pressurise and inflate the boot when required. Inflation is typically for a few seconds every few minutes when the system is being automatically controlled; manual control is typically also available.