the flow rate $F_{\mathrm{g}}$ through the gap as percentage of the total flow rate $F_{\mathrm{t}}$, as a function of gap height $H_{\mathrm{g}}$, for a mask with viscous porous resistance $C_{\mathrm{m}}=2000\, \mathrm{m/s}$, gap length $L_{\mathrm{g}}=1\, \mathrm{cm}$ and different gap widths $B_{\mathrm{g}}$; lines represent analytical predictions and points represent simulation results []{data-label="FIGFt0Fg"}](images/Lg1Cm2000/compareFt-0.0005_Fg0Ft.png "fig:"){width="\factor\linewidth"}\
Flow rate $F_{\mathrm{t}}=95\, \mathrm{L/min}$\
![Analytical predictions and simulation results for the flow rate $F_{\mathrm{g}}$ through the gap as percentage of the total flow rate $F_{\mathrm{t}}$, as a function of gap height $H_{\mathrm{g}}$, for a mask with viscous porous resistance $C_{\mathrm{m}}=2000\, \mathrm{m/s}$, gap length $L_{\mathrm{g}}=1\, \mathrm{cm}$ and different gap widths $B_{\mathrm{g}}$; lines represent analytical predictions and points represent simulation results []{data-label="FIGFt0Fg"}](images/Lg1Cm2000/compareFt-0.001583333_Fg0Ft.png "fig:"){width="\factor\linewidth"}

Figure \[FIGFt0Fg\] shows that the flow rate through the gap between mask seal and face depends non-linearly on the gap height $H_{\mathrm{g}}$. The predictions from the simple analytical model from Sect. \[SECtheory\] agree well with the more sophisticated 2D-flow simulation results.

Figure \[FIGFt0FgLOG\] shows that gap heights of $H_{\mathrm{g}} \approx 0.1\, \mathrm{mm}$ or less are required so that less than $1\%$ of the air flows through the gap. Figure \[FIGFt0FgLOG\] also shows that even a gap of height $H_{\mathrm{g}} = 0.2\, \mathrm{mm}$ (which corresponds to the height of 