The problem is the filter that you should change every six months. Here requires the company. For a scrap of fabric outrageous 14 euros (!!!). This was about a year ago by 2/3 made thinner again so that you can even see through. Of course it is not anti-bacterial, but would not even filter dust.
I instead bought this felt:
PSC = 1
and cutting to him accordingly. Now, instead of 14 € I pay just 40 cents for the same filter performance. That is 30 times less! From the company that is a pure rip off customers.