In Spiral Wound Membranes there are different types and applications according to their pore size. 

( 1 ) Reverse Osmosis Pore Size : < 100 Da Applications : salts removal, small organic molecules 

( 2 ) Nanofiltration Pore Size : 0.1 - 5 kDa Applications : viruses removal, 2- valent ions, Dye Purification 

( 3 ) Ultrafiltration Pore Size : 5-5000 kDa Applications : removal of bacteria, macromolecules, proteins, larger viruses 

( 4 ) Microfiltration Pore Size : > 5000 kDa Applications : removal of larger bacteria, yeast, particles