One of the most common — and surprisingly effective — materials were 600-thread count pillowcases or fabric similar to flannel pajamas when doubled up. Scientists found that, when folded into four layers, high-thread count pillowcases offered up to 60% filtration. Using HEPA furnace filters and vacuum cleaner bags were also among the best homemade alternatives. For reference, the typical surgical mask filters out 62-65% of particles while N95 masks, the ones that are recommended only be reserved for health care workers, filter out 95% of particles.
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