Sterile, individually packaged filters have long become standard for routine microbiological quality control because of the user benefits they offer. They are pre-sterilized and ready-to-use and save preparatory time. As they are individually packaged, they avoid the possibility of contamination of remaining filters in opened packs and conform with GLP, having filter identification and lot number printed on each individual envelope.The increasing demand on these filters required the construction of a new packaging machine with ultra-modern stamping. Each membrane is checked to ensure it is not damaged in any way, is positioned correctly with no slippage under the edge seal, has perfect grid printing and is free of particles. Each envelope is checked for readable lettering.These membrane filters are in accordance with the following norms: ISO 7704, ISO 7899-2, ISO 8199, ISO 9308-1 and EN 12780. In addition to this they have been manufactured for use especially at the same time with Sartorius Nutrient Pad Sets in accordance with many international regulations and recommendations: international pharmacopoeias, DIN and ISO Standards, the American Standards for Water and Foods, mineral water regulations, brewery guidelines, such as MEBAC or EBC, and recommendations of the food industry, such as LMBG, NCA and ICUMSA.All membranes are made of cellulose nitrate (cellulose ester), a material which assures effective retention with high flow rates and optimum colony growth. The printed grid divides the filtration area into 130 squares, each measuring 3.1 × 3.1 mm makes the counting easier, especially for higher bacteria counts and for micro-colonies, but does not influence the growth. The various filter colors allow the best contrast to the colonies or particles.