Our company has issued Nomex cold weather clothing and gear for working outside in the arctic in Alaska'a North Slope (-40F or worse in the winter) for the last 13 years or so. Some divisions have been using it for much longer. At first we all hated it, but we've come around. There are rules about what kind of underlayers you can wear for fire safety and we have witnessed first hand that the Nomex works well in fire and poly doesn't. It is warm, but takes a bit of getting used to if you work hard and risk sweating. It doesn't breathe the same as other fabrics. You also have to keep it clean to maintain the fire resistance. Oil and grease will ruin the fire retardant properties.
DuPont's website may have the information on what combinations work.
http://www2.dupont.com/Nomex/en_US/u...rotection.html
I hope this is useful, back to reading.....