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My suspicion is that the manufacturers intentionally silylate the glass so that it will bond with the silicone skirt. ( https://onlinelibrary.wiley.com/doi/abs/10.1002/hlca.19820650610 ) Problem is, that would make the glass fog. They won't say.
I have noticed that a mask that has been cleaned so it absolutely will not fog must be cleaned again if kept in a plastic bag for a few months. I think it is something the silicone offgasses.The glass is not syliated. They do not want the glass to bond to the skirt. This should be obvious because that would make lens removal almost impossible. The culprit is residual mold release agent. Good luck getting the manufacturers to clean that off for you.
Could very well be. Didn't take long to go down that rabbit hole. Came up with some interesting stuff:The culprit is residual mold release agent.
Comet works well, we used to keep it at the poolside, until someone decided not to rinse their mask b4 putting it on.