Why does the pre-filter turn a darker color?

The textile pre-filter frees the air from large particles. Over time, these particles settle on the surface and are more visible on the light gray ROGER Little pre-filter than on the dark gray pre-filter. Wash the textile pre-filter at 30° C on a delicate cycle and the dark marks will disappear.

Although the dust is less visible on the dark grey pre-filter, we also recommend vacuuming it regularly and washing it after a few weeks on a delicate cycle at 30° C.