finally ME,

I use the TYVEK only for shoulder season here in Colorado. In snow my camp outfit is insulated bibs and anld GoLite 6 month night parka.

I was trying to answer for TN. I have use the outfit I described down to 15 and was comfortable.

I gues the short answer is - I do not know.
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"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra