LifeStraw filters (LifeStraw, LifeStraw Go) use hollow fiber membrane micro filtration with a 0.2 micron pore size. LifeStraw purifiers (LifeStraw Family and LifeStraw Mission) use hollow fiber membrane ultra filtration with a 0.02 micron pore size.
This means that dirty water goes into the LifeStraw, microorganisms are physically removed and safe drinking water comes out. Imagine really small tubes with even smaller pores that trap contaminants, but allow water to flow through. All LifeStraw products do not use chemicals, do not require pumping and do not require any energy input (like batteries).