Would a 2 ply doubled over bandana covering nose and mouth be as effective
I don’t know.
But any mask is likely more effective than nothing.
The mask does 3 things.
It prevents particles from entering the air when you cough or sneeze or talk. And even if you feel well, you could be a carrier and not know it.
It prevents you from touching your mouth or nose.
It blocks some of the particles from getting to your mouth and nose, thus reducing the size of the initial infection, giving your body more time to respond. Which can keep the severity of the illness lower.