Clean rooms are very special rooms designed to keep contamination as low as possible.  Some work projects cannot be completed in a typical environment.  If normal conditions would pose a threat to the project, then a safe room will need to be put into place and maintained.  There are different levels of clean rooms, but none are truly sterile.  Their goals are to reduce air pollution to certain amounts, not to ensure absolute sterility.  

Workers must use special supplies in clean rooms in order to keep contamination below a certain level. Regular objects typically cannot be brought in from outside. Special supplies specifically made for clean rooms are used instead. Cleanroom Supply Connection and some
other companies sell products for this purpose. Cleanroom clothing, paper, pens, wipes, and gloves are examples of items that can be
created for use in these special environments.
Properly supplying the clean room is not the only concern. They must also be properly maintained every day in order to control
contamination levels. The level of the clean room is determined by the sensitivity of the project. More sensitive projects, like the Hubble
telescope, will need more stringent contamination control than some other projects. There are many devices and systems used to keep the air as free of debris and other contaminants as possible. HEPA filters, ULPA filters, air locks, and air showers are examples of systems that
may be put into place.
Workers must also abide by certain rules. For example, clean room employees might not be allowed to wear makeup or other products at work. Beauty products, perfumes and colognes, and certain other items have caused damage to sensitive projects before.
Clean rooms can differ based on the needs of whatever they are working on. However, they share the practice of minimizing pollutants and contaminants from the outside world. Special supplies, systems, and rules are therefore put into place to meet this objective.