Outdoor air also contains impurities, especially in urban environments. This means that outdoor air must be cleaned before it is used indoors. Filters prevent impurities from entering indoor air.

Filtering is needed for, above all, health reasons and greater comfort. Also, the operation of ventilation systems, many manufacturing processes, and sensitive equipment requires clean air in their surroundings. Clean, filtered air is always required when people’s health and well-being, or the quality of production and productivity, is involved. The purity of air, cleanliness of rooms, quality of products, and operability of equipment can be crucially influenced by choice of appropriate air filters.