The idea is "most likely" to neutralize any chemical elements that would land on such a suit.
It's sounds like a poor man's method of making the old style of US military suits that we had to wear under our slicker suits along with the masks, gloves and boots.
Does anybody else here remember those old NBC suits?? I do, they had an oily feel to the fabric, were hot, and scratchy. It was like wearing some kind of oiled woolen clothing.
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QMC, USCG (Ret)
The best luck is what you make yourself!