All nine FFR models demonstrated differences in their number of media layers and the hydrophobicity of their filter media (Table 5 ). Common to all three models of surgical N95 respirator was the fact that their outer layer was hydrophobic. This is not surprising since surgical N95 respirators cleared by the US FDA undergo fluid resistance testing and are used as barriers against disease transmission by airborne respiratory fluids, including blood, and other small infectious droplets (Bailar et al., 2006) . The N95 FFRs and P100 FFRs varied by having either hydrophobic or hydrophilic outer and inner layers. All middle layers, with the exception of those that were plastic webbing, were hydrophobic on both sides.