As in the short term experiment, mask type was a strong determinant of protection (Table 2 ). Protection factors for each type of mask were similar to the protection factors measured in the short term experiments for adults. There was considerable variability between volunteers. The median protection factors measured over a 3 hour period increased for those wearing homemade masks, decreased for those wearing FFP2 masks, and did not show a consistent pattern for those wearing a surgical mask (Figure 2 ), but overall protection factors calculated per type of mask were stable over time, and did not change statistically significant with prolonged wearing. Overall, protection factors were relatively stable over time for each individual (ANOVA p = 0.4). Males and females did not have significantly different protection factors (ANOVA p = 0.9). As in the short term experiment, protection conferred by surgical masks was higher than protection given by a home-made mask, and protection provided by a FFP2 masks was again markedly higher than protection provided by a surgical mask. As in the short term experiment, more strenuous activities (reading and walking) tended to increase the protection of the home-made mask and to a lesser extent of the surgical mask, and decreased the protection by the FFP2 mask, but there was no overall significant effect of type of activity on PF (ANOVA p = 0.1). Outward protection experiment