BigCityHillbilly wrote:
"I'd like to know what you think of polypropylene and fleece as opposed to wool."

I live in polypro and fleece all winter. It works. I wear wool too, but usually with a polypro layer underneath, which is more comfortable, easier to wash, and hangs-to-dry. Synthetics manage moisture much better than woolies, and that's the key to staying warm.

But industrial oilfield sites are another matter entirely. Polypro and fleece are effectively banned -- unless they are factory-treated with an approved flame-retardant substance. This is done for good reason: synthetics, in a fire, turn into a super-hot goo that bonds permanently with human skin, and create the most horrific injuries you can imagine. Wool and cotton, on the other hand, provide a degree of protection.

If you were choosing clothing to protect you during the crash of an airliner, you would surely not wear synthetics. Oilfield workers face similar hazards.