The percentage or ‘media’ determines what the oil, air or fuel has to pass through and where the dirt is trapped. Working on the theory of a tortuous path, the more twists and turns a particle of dirt has to take, the more likely it is to be captured.
Dust-holding capacity of the filter determines how long its life is. The more high-quality paper inside the filter means the more dirt it will hold and the longer it will last.
Minimising resistance to flow ensures the engine is never starved of air, oil or fuel. Poor flow in a filter deprives engines of their vital needs, causing them to work harder, lose power and create rapid engine wear over shorter periods.