i say dont need to work super hard on this. just wear double mask and yr problem solved. I say this is common sense.

if u find it hard to breath in ur mask, it is 99% working. When u cannot take oxygen from outside air when wearing mask, it is clearly been filtered or blocked. It is a very good reminder that you dont stay too long outside.

If its somehow easy to breath, maybe 95% or less working, depending on your needs. I know it is a weak judgment but it will work.

all these local made mask brand, lol up to you if you want to buy to 'relieve your worry'.