A kraft paper in which 75 per cent of the volume is filled with cellulose (ε2 ¾D 6ε0) should be impregnated with mineral oil (ε1 ¾D 2.2ε0). Then v1 D 25 per cent and εres ¾D 4.19ε0, which is less than one could expect by a merely linear interpolation.