Pore Density

Track-etched membranes are made differently from other filter types. They start with a transparent polymeric film which is integral – nothing passes through it – which then goes through a series of radiation and chemical treatments that open up holes straight through the material. What becomes important in terms of filter characteristics of a track-edged membrane is the number of pores per unit surface area.

Consider a piece of material with 100 pores per cm². This material would have twice the filtration capacity of a piece with only 50 pores per cm². Pore density is measured by placing a membrane sample under a scanning electron microscope (SEM) and physically counting the number of pores per unit surface area. Track-etched membranes of the same pore size can exhibit a gradient of different filtration rates dependent upon the pore density.