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. 2021 Feb 19;70(7):254–257. doi: 10.15585/mmwr.mm7007e1

FIGURE 2.

This figure is a bar chart showing the mean cumulative exposure for various combinations of mask wearing for a source and a receiver headform, including no mask and no mask, no mask and mask, mask and no mask, and mask and mask for unknotted medical procedure masks, double masks, and knotted/tucked medical procedure masks.

Mean cumulative exposure* for various combinations of no mask, double masks, and unknotted and knotted/tucked medical procedure masks†

* To an aerosol of 0.1–7 μm potassium chloride particles (with 95% confidence intervals indicated by error bars) measured at mouthpiece of receiver headform configured face to face 6 ft from a source headform, with no ventilation and replicated 3 times. Mean improvements in cumulative exposures compared with no mask/no mask (i.e., no mask wearing, or 100% exposure) were as follows: unknotted medical procedure mask: no mask/mask = 7.5%, mask/no mask = 41.3%, mask/mask = 84.3%; double mask: no mask/mask = 83.0%, mask/no mask = 82.2%, mask/mask = 96.4%; knotted/tucked medical procedure mask: no mask/mask = 64.5%, mask/no mask = 62.9%, mask/mask = 95.9%.

† Double mask refers to a three-ply medical procedure mask covered by a three-ply cloth cotton mask. A knotted and tucked medical procedure mask is created by bringing together the corners and ear loops on each side, knotting the ears loops together where they attach to the mask, and then tucking in and flattening the resulting extra mask material to minimize the side gaps.