1. Compatible models: The 4-piece replacement filter is compatible with the Xiaomi 4th generation air purifier replacement filter. Please check the required model and size again before placing an order to avoid purchasing errors. 2. High-quality materials: The 4-piece replacement filter uses a high-density pre-filter, which is fold-resistant, oil-resistant, acid-resistant, and can intercept large particle pollutants; the H13 HEPA filter has uniform spacing and clear folds, which reduces wind resistance and allows rapid air circulation. 3. Fresh air: The high-efficiency activated carbon is evenly filled, increasing the contact area between the gas and the activated carbon, and improving the air purification and deodorization effect. 4. Regular replacement: With the number of uses and the passage of time, the cleaning performance of the Xiaomi 4th generation air purifier filter will gradually decrease, and even cause secondary air pollution. Therefore, it is recommended that you replace the Xiaomi 4 filter every 6-12 months.