Very interesting summary of the effectiveness of face shields [1]
"Utilizing a cough aerosol simulator loaded with influenza virus (aerosol volume mean diameter of 8.5 μm) and a breathing simulator, Lindsley et al.[16] reported 96% and 92% reductions in the risk of inhalational exposure immediately after a cough for a face shield at distances of 18 in (46 cm) and 72 in (183 cm), respectively. Decreasing the aerosol size to 3.4 μm resulted in the face shield blocking 68% of the inhalational exposure at 18 in (46 cm) immediately after the cough and 23% over 1–30 min post-cough (during which time the larger aerosol particles had settled out and droplet nuclei had formed and remained airborne so that flow occurred more easily around the edges of the face shield)"
Seems like a face shield may be very good protection for a short term exposure - especially combined with a mask. e.g. walking by someone who coughs.
It also makes me wonder about a face shield fixed with something to blow filtered air in from the top of the shield. I assume that would make it less likely for air to come around the edges of the mask and possibly be more comfortable than a mask. You could have a shield blowing a constant cool breeze on you. Although this would have the disadvantage of needing batteries and replacing filters.