Paper is usually used for the filtration of liquid, gas and air and the paper types are divided into two main groups.

1. The first category is composed of cellulose-based fibers. The maximum and average diameter values of the holes between the fibers determine the micronic class of that paper. They have the values between 5 and 50 microns.

2. The second category involves polyester based materials. These are weaved from polyester fibers. They have 15-20 microns of pore values.
According to the kind of fluid which will be filtrated, and depending on the working conditions of the place that the filtration will take place, the technical properties of the motor and the air temperature of the environment; the properties needed for the preferred filter paper are;

The weight of the paper
The efficiency of the paper
The percentage of resin
The thickness of the paper
The flowing rate of air
The air permeability
The explosion resistance
The resistance
The pore diameter

In addition, during the production of filters, in order to prevent the filter paper from tearing apart and moving into the system in pieces, protectors that are made up of perforated metal sheet are assembled to inner and outer parts of the filter.