###### Abstract  
During the COVID-19 pandemic, reusable masks became ubiquitous; these masks were made from various fabrics without guidance from the research community or regulating agencies. Though reusable masks reduce the waste stream associated with disposable masks and promote the use of masks by the population, their efficacy in preventing the transmission of infectious agents has not been evaluated sufficiently. Among the unknowns is the effect of relative humidity (RH) on fabrics' filtration efficiency (FE) and breathability. This study evaluates the FE and breathability of several readily accessible mask materials in an aerosol chamber. Sodium chloride aerosols were used as the challenge aerosol with aerodynamic particle diameter in the 0.5 to 2.5 \(\upmu\)m range. To mimic the variability in RH in the environment and the exhaled-breath condition, the chamber was operated at RH of 30% to 70%. The face velocity was varied between 0.05 m/s and 0.19 m/s to simulate different breathing rates. The FE and pressure drop were used to determine the quality factor of the materials. Among the tested materials, the 3M P100 filter has the highest pressure drop of 140 Pa; the N95 mask and the 3M P100 have almost 100% FE for all sizes of particles and tested face velocities; the surgical mask has nearly 90% FE for all the particles and the lowest pressure drop among the certified materials, which ranks it the second to the N95 mask in the quality factor. Other material performance data are presented as a function of relative humidity and aerosol size. The quality factor for each material was compared against reference filtration media and surgical masks. Multiple layers of selected materials are also tested. While the additional layers improve FE, the pressure drop increases linearly. Additionally, the certified materials performed approximately three times better than the highest performing non-certified material. m 2022 aca 2022 aca 2022 aca 2022 aca 2022 aca 2022 aca 202  
depends on the particle size and the type of filtration media. Gravitational settling is prevalent in removing droplets \(\mathrm{d_{p}}>50\)\(\mathrm{\SIUnitSymbolMicro m}\). Inertial impaction is primarily seen on aerosols larger than 1\(\mathrm{\SIUnitSymbolMicro m}\), whereas diffusion primarily affects the smallest particles [12]. As the flow rate increases, so does the effect of interception and inertial impaction, while the gravitational settling, diffusion, and electrostatic attraction become less impactful. Face masks should provide the wearer with high filtration efficiency (FE), while remaining comfortable. Mask comfort can be attributed to the fit of the mask, a mask's ability to transfer heat and moisture away from the face, and its breathability [13]. Breathability is described by the permeability and pressure drop across the material [13; 14]. Part of the certification testing for mask materials that public health organizations, such as the National Institute for Occupational Health (NIOSH), conduct is testing a materials pressure drop. Materials may not exceed the pressure drop values at the corresponding flow rate to ensure the breathability of the mask. Respirators can reach pressure differentials ranging from 210 to 350 Pa, whereas surgical masks should range between 40 Pa/cm\({}^{2}\) and 70 Pa/cm\({}^{2}\)[14; 15]. At the start of the COVID-19 pandemic, high demand resulted in a scarcity of masks [16; 17; 18; 19], leading to many using homemade masks made from various textiles. However, the protection from aerosolized transmission provided by these masks remains unclear, and the public has not received clear guidance from health officials. Previous studies compared the performance of homemade masks and those certified by organizations such as NIOSH [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44]. However, the accuracy of the results and the methodology used by some of these studies have come under scientific scrutiny [14; 45; 46; 47].