Lab air filters are used to filter the air to remove unwanted substances such as dust and pollutants and to clean the air by removing vapors or gases. Air filters come in many different types and designs. Their porosity is around 70%–99%, and this is significantly more in filament filters with fiber sizes ranging from micrometers to 100 µm. In a porous filter, the porosity is about 50%–90%; they have high efficiency and greater pressure drop than other filter types. Capillary porous membrane filters are useful for collecting particles from smooth surfaces such as scanning electron microscopes. Cloth filters are useful for cleaning high concentrations of dust and are used in industrial cleaning. The simplest form of cloth filter is the vacuum cleaner used in the home. Air filters are widely used in pharmaceutical factories, hospitals, operating rooms, laboratories and in the food and microelectronics industries.