i've seen one made out of cheesecloth and masking tape.  The guy had written "placebo" on the top edge of the mask on the Some dude was required to wear one at a hell mart.  He pushed the issue until the cops were going to be called.  he pulled the cheesecloth mask out and put it on.  They were satisfied and left him alone then.  it's not about health.  It's about compliance.