How often do you change these filters? Couldn't find it on 3M site, but saw comment that said 6 months after opening. I only use them that often. I use them for
3M™ Particulate Filters | 3M United Kingdom
3M Xtract™ Clean Sanding Solutions | 3M United Kingdom
2 Piece 3 M Filter dusts Article Nr,6035 P2 Mask for P3 Series 6000 / 7000 : Amazon.co.uk: DIY & Tools