Table 2

The effective diameter (µm) of pores for each layer of three different masks based on reflected light images

Effective diameter (µm) of mask pores
Back up filterForeign-manufacturedUS-manufactured
Layer 125.129.427.2
Layer 223.711.025.4
Layer 3Too small to measure*56.6Too small to measure*
Layer 459.026.417.5
  • Foreign-manufactured mask that failed particle filtration efficiency testing was found to have the smallest pore size of 11 µm.

  • *The masks that passed had smallest pore sizes that were much smaller than 11 µm, beyond the capability of the microscope to reliably resolve for measurement due to the tightly woven fibres and overall material density.