Polyester Fiber Pre-Filter for Initial Air Filtration A pre-filter designed for initial filtration at the front end, constructed from high-quality polyester fiber filter cotton. Key Features Foldable structure: Features a folding design that increases effective filtration area by 3-5 times compared to flat filters, reducing wind speed and extending service life while lowering system resistance. Filtering efficiency: 5 micron accuracy with European standards G1-G4. Weight