The foam behind the holes in the outlet grille is a soundproofing foam fixed to the outlet grille. It is a fleece or non woven material, only used for acoustic insulation. This material has no significant filter effect.
The outlet grille filter retains 85% of all dust particles bigger than 300 nanometers and creates an air flow of 13 liters per second. The surface of the filter in the outlet grille is 300 cm².