## 1 Introduction
The two parameters that are used to measure the efficiency of a face mask are (1) filtration efficiency (F), the particle transmission reduction, which reduces the penetration of airborne particles from coming into contact with the wearer, and (2) breathability, which is measured as a pressure drop through the mask [15]. These two factors are combined into a single measure called a filtration quality factor (Q) to assess mask materials [15]. Thus, the efficiency of a face mask would depend on a combination of the particle's size, shape, and charge with the physical properties of the materials used to fabricate the mask, such as the thickness and packing density of fibers, the pore size between the fibers, and the fabric texture (non-woven or woven) [16]. Also, from a fluid mechanics point of view, external factors such as velocity airflow and frequency of respiration have been shown to have an impact on the F of masks [17; 18]. Aerosols have different capture mechanisms for preventing penetration through masks. For example, gravity sedimentation, inertial impaction, interception, diffusion, and electrostatic attraction [7; 19]. For particles <1 \(\upmu\)m, the dominant mechanism is still impaction. Diffusion becomes predominant only for particle sizes below the most penetrating particle size (MPPS) (typically in the order of 300 nm) [20]. [PERSON] et al. (2020) have claimed that the flow rate and F of a face mask are inversely proportional to each other. Thus, by increasing the flow rate, the F of a face mask can decrease [21]. A similar conclusion was made by [PERSON] et al. (2006), who stated that as the flow rate increases, the penetration of particles through the face mask increases [17]. However, filtration efficiency is also dependent on the size of the particles. For instance, the removal of smaller particles is better at low flow rates [22]. In particular, by increasing the airflow velocity, the F of face masks for small particles decreases while increasing for larger particles [23; 24]. This phenomenon is due to different mechanisms of particle penetration [25; 26]. In addition to this, high flow rates can enlarge the pores in a material, thus allowing more particles to pass through it. Several studies have compared the F of a range of woven materials, including synthetic (e.g., polyester, nylon) and natural (e.g., cotton, silk) materials, to non-woven materials such as polypropylene, the material that has been used for _FFP3_, _FFP2_, and _Surgical_ masks [16; 27; 28]. Different materials were tested using an automated filter tester (TSI 8130, TSI Inc., Shoreview, MN, USA) at a range of different flow rates (32-85 L/min) to simulate air flow at low and high intensities. The size of the processed NaCl particles was between 0.075 and 0.1 \(\upmu\)m since most respiratory viruses such as influenza and SARS-CoV-2 fall in this size range (SARS-CoV-2 virus particles measured about 0.120 \(\upmu\)m) [29; 30]. Aerosol particles will contain more virus when they are larger than the virus. These studies showed that woven cotton fibers with finer fiber diameter and high porosity have lower F (\(\sim\)20%) and pressure drop (\(\sim\)14 Pa) compared to wider woven cotton fibers with low porosity. However, multi-layered cotton fibers woven to a high density with non-apparent yarn-to-yarm gaps between threads, showed better filtration properties (\(\sim\)26%) than randomly oriented polyester fibers. Although the number of polyester layers increases, the pressure differential increases. Woven silk fibers with larger yarn-to-yarm gaps have shown low F (\(\sim\)5%) and low pressure drop (\(\sim\)7%) [16; 27; 28]. Melt-blown polypropylene fibers used in _FFP2_, _FFP3_, and _Surgical_ masks are layered to form a tangled structure of randomly arranged fibers capable of trapping particles effectively and allowing for good breathability [31]. Typically, \(\sim\)95% F with \(\sim\)9 Pa pressure drop is seen for _FFP2_ and _FFP3_ masks, and \(\sim\)34% F with \(\sim\)34 Pa pressure drop is seen for _Surgical_ masks.