The Center For Disease Control (CDC) usually recommend face masks with the filtration certification standards such as N95, KN95, FFP2 or above.
Our METRO-MASK: URBAN is KN95 certified which is similar to FFP2 and N95, and is therefore a good mask in the aspect of Sars-Covid-19. Please see the comparison between the different classifications here.
Viruses are extremely small particles but are airborne by traveling on other larger particles, which is how filter masks give protection. However, note that no mask can guarantee full safety and protection agains viruses.
The protection against viruses depends on the particle size of the aerosols containing infectious viruses. The sizes of these virus-containing particles differ from just the naked virus diameter (0,02–0,03 µm) to the sizes of the carrier particles. According to a study of the influenza virus, the virus-containing particles vary largely in size and 5% of the particles where larger than 4 µm, 75.5% was 1–4 µm and 19.5% smaller 1 µm. In another study of FMDV, 65–71% of the virus-containing particles were over 6 µm in diameter, 19–24% was 3 - 6 µm and 10–11% were under 3 µm.