Filter Cloth Specifications

Filter cloth is used in numerous areas. Face masks, air filters and water filters are a few examples that use a cloth filtration system. The cloth that filters use have numerous specifications, but follow some basics rules. The standard specifications for a cloth filter include the filtration level, efficiency and strength.
Filtration Level
The filtration level is measured in microns. A micron is another term for micrometer. The micron level is the smallest particles a filter cloth can capture. A rating of 10 microns means the filter is capable of catching and holding particles that are 10 micrometers is diameter. A human hair is 70 micrometers. Most bacteria is between 1 and 10 microns.
The micron level is not an absolute, however. The cloth is capable of capturing particles of that size but it is not guaranteed that the filter will catch those particles.
Efficiency
The efficiency rating is where the filtration levels are accurately measured. An efficiency rating of 50 percent at 10 microns means that the filter will capture approximately half of all particles 10 microns in size. This is called a nominal rating.
An absolute rating is given to a filter bag that is capable of capturing 98 percent or higher of the measured micron level. The best filters will have a high efficiency rating for the size particles that are meant to be filtered. Dust particles are often 10 microns or higher, meaning liquid filters given an absolute rating at 10 microns are very good filters. Face masks given a nominal rating at 10 microns are highly ineffective.
Strength
The cloth filter is measured for tensile strength and bursting strength. Filtration levels are secondary to the strength measurements. Liquid filters, such as those found in oil filter fabric, are measured for both strength and filtration ability. The flow is measured in pounds per square inch (PSI) and is dubbed the pressure rating. Tensile strength is measured in pounds. The specifics of the measurements depend upon the type of fabric and the purpose of the fabric.
An absolute rating of 1 micron does not imply a strong filter. Cloth filters used in face masks typically only face airborne contaminants and do not need heavy strengths.
Liquid filters, however, have to endure the high pressures associated with the flow of liquid. Submerged cloth filters, such as landscaping fabric, have to be able to withstand heightened pressures from foot and vehicle traffic on the ground surface.