... permeability, high filtration efficiency, low resistence, big cubage, compact structure and so on.Outer paper Grammage: 45g/sq meter~ ... permeability, high filtration efficiency, low resistence, big cubage, compact structure and so on.Outer paper Grammage: 50g/sq meter~ ... permeability, high filtration efficiency, low resistence, big cubage, compact structure and so on.Outer paper Grammage: 50g/sq meter~ ...