Main Parameters and Testing Methods of Industrial Filter Paper

Industrial filter paper is widely used in the fields of hydraulic systems, engine filtration, air purification, and industrial dust removal. Its performance is evaluated by three main technical indicators: filtration performance, physical properties, and mechanical strength.

Two sheets of industrial filter paper of different colors

Table 1: Filter Paper Performance Indicators and Testing Methods
Category	Indicator	Description	Test Method
Category	Indicator	Description	Instrument	Standard
Filtration Performance	Filtration Efficiency	The ability of the filter paper to capture particles of a certain size, expressed as a "Dn" rating (e.g. D95 means 95% capture of that particle size).	Filter media efficiency testing system (includes a dust generator and particle counter).	GB/T 6165 (for air filter paper), ISO 16889 (for hydraulic fluid filter paper).
	Air Permeability	The air volume passing through a unit area of filter paper per unit time under a set pressure difference (L/m²·s), indicating airflow ease.	Air permeability tester (typically at a fixed pressure of 20 mm H₂O).	GB/T 5453
	Air Resistance	The pressure drop at 85 L/min airflow through 100 cm² of filter paper (mbar or mm H₂O).	–	ISO 9237
Pore Structure	Maximum Pore Size	The largest single pore size present in the filter media, typically measured in micrometers (μm) or nanometers (nm).	Pore size analyzer (using the bubble point method or mercury intrusion method).	GB/T 1038 (bubble point method) ISO 15901 (mercury intrusion method).
Pore Structure	Mean Flow Pore Size	Mean flow pore size (MFP) is defined as the average diameter of the pores in a porous material	Pore size analyzer	ISO 15901 (Mercury intrusion method).
Physical Properties	Basis Weight	Mass per unit area (g/m²), influencing filter paper density and strength; Typical industrial range: 20–140 g/m².	Electronic balance (with an accuracy of ≥ 0.1 mg) and a standard cutter for sampling 100 cm² areas.	GB/T 451.2
	Thickness	Permeability thickness under a set pressure (e.g. 2 kPa) in mm, affecting dust holding and flow resistance; Typical range: 0.12–0.49 mm.	Thickness gauge (with a presser foot diameter of 20 mm).	GB/T 451.3
	Corrugation Depth	Pleat or groove depth (about 0.2 mm), which improves the media’s longitudinal stiffness.	–	Enterprise standard
Mechanical Properties	Stiffness	Bending resistance (mN·m); Adequate stiffness ensures filter pleats maintain shape and avoid collapse (e.g., in bag filters).	Stiffness tester (using a three-point or four-point bending method, with a bending angle of 15° – 30°)	GB/T 22364 (paper and board), ISO 5628 (paper and board – bending resistance).
	Burst Strength	Rupture strength (kPa), indicating resistance to uniform pressure; Crucial for liquid filtration pulses, typically ≥ 300 kPa.	Burst tester (hydraulic type for simulating liquid pressure, pneumatic type for simulating air shock).	GB/T 454 (paper – bursting strength).
	Wet Tensile Strength	Wet tensile strength, essential to prevent filter paper rupture during operation.	Tensile tester. The sample is saturated with water prior to testing.	GB/T 12914 (paper and board – determination of tensile properties).