This TIP describes the methods and procedure for the measurement of press fabric permeability to water. The method is suitable for the evaluation of fabrics on the run without interrupting the operation of the paper machine. This technique could be used to follow changes in fabric permeability which occur during fabric life. The method can be used to measure the cross direction (CD) permeability profile and machine direction permeability variation as well as identify localized areas of high or low permeability. Felt permeability data can be used to identify and optimize operating parameters such as felt life, specific areas that require cleaning or general felt cleaning procedures, press dewatering, nature and frequency of chemical cleaning, or electrical power to drive vacuum pumps and presses. These parameters all have direct effects on key paper machine performance indicators such as sheet moisture entering the dryer section, machine speed and finished product quality.