In automobiles, there are 8 to 15 different filter elements. A wide range of specifications are needed depending on exactly where in the automobile or engine the filters are used, and what directives are in place in the country of use. It is important to note that some of the filter media are not changed throughout to whole life of the car. There are also a large number of filter elements, which require routine maintenance. Studies in 2006 assumed that an annual replacement of approximately 1.93 billion filter elements could be expected. Their working temperatures vary between 40c and 1000c. The filter media themselves are made of impregnate papers on a cellulose base and nonwovens made from synthetic fibres, ceramics, metal, fabrics and porous sintered metals. In addition to filtration, some filter elements in automobiles provide acoustic dampening and energy absorption in a crash. Filters are also used for the filtration of impurities such as pollen grains, dust particles, etc. from the air that is supplied to the passenger cabin of an automobile. The filters used in these sectors need to possess the property of high particle separation efficiency using less pressure drop along with good mechanical and thermal properties. Filters in the automotive sector are a combination of active carbon and conventional filter media. These hybrid filters comprise up to 500 g active carbon per m2.