New version features a multilayer urethane material instead of the OEM high density paper material. The use of urethane dramatically improves filter efficiency. This filter cannot be washed and re-used. Replace with normal recommended factory intervals. Upon full opening of the throttle, a huge volume of air is drawn in at high speeds. Meanwhile, when the throttle is closed, an inertial force acts and air is compressed at the instant just prior to full closing. When the accelerator is subsequently depressed, the sealed cleaner box is subjected to a more intense vacuum as a result of the reaction to compression. The efficiency of replenishment is increased a result of this action, and accordingly, the air-intake system of the Honda NA is both extremely ingenious and highly necessary