The Frazier Differential Pressure Air Permeability Instrument has been the standard in the industry for measuring air permeability for many years. The term “Frazier Number” (or CFM as some people refer to the number as) has developed over the years in regard to permeability or porosity because of popularity of the this Instrument. People actually use this term with different definitions depending on the application, so therefore what one company or industry may call the Frazier Number may mean something different to another. Because of the multiple industries that use the instrument, strictly speaking there is no specific definition. In some cases people will use the Frazier Number to describe airflow but not give the differential pressure at which the airflow was taken. Usually in these cases the differential pressure is set to 0.5 inches of water due to industry standards but this is not always the case. In other cases, people will use the results given by the instrument but will have modified the test sample opening size and therefore have a repeatable number but will no correlate with the standard one square foot of sample area.
The Frazier Differential Pressure Air Permeability Instrument’s permeability readings are “rates of flow of air in cubic feet per square foot of sample area per minute.” Therefore many, but not every time, when someone mentions a “Frazier number” (or in some cases CFM) it is most likely this specific reading at a differential pressure of 0.5 inches of water as the commonly set variable.
Many times a Frazier Air Permeability Instrument out in the field is simply referred to as a “Frazier”. There are other permeability instruments however, and you must be careful as they do not necessarily correlate with the Frazier even though they may be called a “Frazier” type permeability instrument.
Our instruments are very reliable and have a very good repeatability of readings even from instrument to instrument and location to location. This is what people have come to expect when referring to the “Frazier” in testing air permeability.