European Standard G1/G2/G3/G4 Air Pre Filter With 95% Weight-Based Detection Efficiency Product Description Foldable structure: Adopting a folding design, it significantly increases the effective filtration area of the filter material (compared to flat-type filters, the filtration area can typically be increased by 3-5 times). Under the same air volume, it can reduce the wind speed of the filter material, extend the service life, and simultaneously reduce system resistance.