Microporous Membrane are in structure and function very similar to a traditional filter, with rigid high voidage and randomly distributed interconnected pores.
The sizes of the pores are of the order of 0,001 to 0,1 um. Discrimination is achieved by the pore size, as all particles or molecules larger than the largest pores are completely rejected by the membrane.
All the particles or molecules smaller than the smallest pore pass the membrane completely. All particles or molecules of intermediate size are partially rejected in correspondence to the pore size distribution of the membrane.
With a microporous membrane, only particles or molecules that differ considerably in size can be separated.