"Worst" and "worthless" are not the same thing. Bandanas are the worst. The gaiters just need to be doubled up if they're thin, but even if they're not doubled up they still reduce the spread.
According to this research, they're the best option when not too thin.
UW-Madison engineering professor Scott Sanders has come up with a novel way to test how droplets escape from coughing people wearing masks.
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