These FFP3 NR (D) face masks are intended to protect against solid and liquid particles, according to the UNE-EN 149:2001 + A1:2009 standards. They are suited to protect against extremely toxic and harmful materials in concentrations up to 50x0EL or 20xAPF. OEL: Occupational Exposure Limit. APF: Assigned Protection Factor. (D): Dolomite clogging test for more comfortable breathing. Sold in packs of 5 units. They include highly-resistant adjustable bands and a exhalation valve.