The fabric pre-filter can be removed from the appliance, then washed and refitted.
Details can be found under Stadler roger Mini 40W.

Hello ngochien. Thank you for your comment on our Roger little air purifier. Unfortunately, it is not possible to fit a textile pre-filter to the Roger little of the previous generation. The air purifiers of the current generation are automatically equipped with a textile pre-filter. If you have any further questions, please feel free to contact us directly by email at service@stadlerform.com or by phone on 041 720 48 48. Best regards, your Stadler Form Team