The filter inside an FFP3 mask captures 99% of airborne particles, which is tested, certified, and printed on the packaging. What isn't printed is how much inhaled air bypasses that filter entirely through a gap at the seal.
The HSE sets FFP3 total inward leakage at a maximum of 2%. If it exceeds, the mask's protection is compromised regardless of its filter grade. This is why face fit testing is the only way to know the mask is working.





