# Performance Comparison among KN95-Certified Face Masks by Classical Techniques and Innovative Test
## 3 Results and Discussion  
### Percentage Inthaled Fraction and Breathability  
Table 2 reports the experimental outcomes obtained during the present investigation for all tested samples by means of our newly developed MB method and the breathability test.  
The percentage inhaled fraction is calculated as the difference between the mean R% values of investigated samples and the R% value of the golden standard. A bigger inhaled fraction value corresponds to a higher amount of MB droplets passing through the face mask during the 30 min MB nebulization test and reaching the cotton pad (mimicking the respiratory system in an individual). As general criterion, an inhaled fraction smaller than 10% can be considered as a positive result in terms of both MB droplet filtering capacity and an intrinsically good fit with the head mannequin for the duration of the experiment.  
It is interesting to see how all tested masks have reached different filtration outcomes according to the MB method, thus showing differences despite being all KN95-certified. These results could indicate two possible scenarios: the KN95 certification is not able to discriminate the diffusion of such small droplets passing through the mask, thus potentially reaching the wearer's respiratory system; otherwise, tested masks could be labeled but not validly certified. This is obviously a preliminary consideration, and further systematic tests should be performed.  
For what concerns the masks' breathability, the test consists in the pressure drop measurement between the internal and the external side of each mask, following the UNI EN 14683:2019 standard procedure; results are reported in Table 2. As the pressure drop increases, the air permeability lowers, making respiration more difficult [35]. The pressure drop per unit area (\(\Delta\)P/A) ranged between 43 and 86 Pa/cm\({}^{2}\), and the latter represents a quite high value which implies difficult breathability in the considered respirator. Sample 6 appeared to induce a higher pressure drop compared to the other masks together with sample 7, which reaches a comparable pressure drop with sample 6. Such a result could be related to the structure of the internal layer of this mask. As shown in Figure 2, the central part of the sample 6 was composed of a series of short, interconnected fibers that generated a denser film, compared to the other samples.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \({}^{\mathbf{a}}\)**Diffuse Reflectance R\%** & **Inhaled Fraction (\%)** & \({}^{\mathbf{b}}\)\(\Delta\)P/A (Pa/cm\({}^{2}\)) \\ \hline
0 & 99.5 \(\pm\) 0.9 & 0 (ref) & 62 \\
1 & 98.7 \(\pm\) 1.4 & 0.8 & 54 \\
2 & 89.2 \(\pm\) 1.4 & 10.3 & 69 \\
3 & 81.3 \(\pm\) 1.5 & 18.2 & 43 \\
4 & 93.1 \(\pm\) 2.7 & 6.4 & 61 \\
5 & 84.5 \(\pm\) 3.9 & 15.0 & 51 \\
6 & 75.6 \(\pm\) 3.6 & 23.9 & 86 \\
7 & 88.9 \(\pm\) 1.0 & 10.6 & 81 \\
8 & 78.2 \(\pm\) 7.3 & 21.3 & 58 \\
9 & 86.8 \(\pm\) 1.2 & 12.7 & 63 \\ \hline \hline \end{tabular} \({}^{\mathbf{a}}\) Standard deviation calculated on n = 3. \({}^{\mathbf{b}}\) (8 L/min, 4.9 cm\({}^{2}\)—according to UNI EN 14683:2019).  
\end{table}
Table 2: Diffuse reflectance values measured after 30 min of MB nebulization; calculated percentage inhaled fraction, and breathability values for the set of investigated face masks.