The performance of an air filter is measured according to their trapping capacity and their ability to allow free airflow. Unfortunately, stock filters are unable to cope up with these two functions altogether. This is because stock filters are commonly made from several layers of paper. They have been designed for maximum trapping capacity, compromising air flow. The paper material and the construction of several layers of sheets, make the filter get easily clogged after trapping a certain amount of dirt. Manufacturers have come up with the solution to create an air filter made of cloth or foam. These materials can trap more dirt without clogging easily. This way, only clean air is ensured to pass through the strainer freely.