Ok, I bought a sampler. The shield is bassically a piece of cloth with a breathing hole cut in the middle.
As I said they are cloth which means it is composed of fibers woven in such a way to make a flat piece of cloth. The fact that it is woven means that there are spaces between the woven fibers which means it is porus,(Forced air will flow around the fibers).
So, in my mind, the shield would just turn into one big evenly spread out porus leak that is probably to small to be detected by sound or feel.
Having said that, how can I test them to see if they work without making it dangerous to me?
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REMstar Auto M series with A-Flex and humidifier. Plus an O2 concentrator

