So the only thing I wore, had on me or used in any way that was synthetic were the soles of my boots.
Temps -8/-9c.
No tent, no sleeping bag, no fire by the shelter, no hot water bottle or hot rocks....
Gear:
Wool blanket, thin wool cloak with hood, reindeer skin, fur coat, fur hat. Flint and steel for fire. (Just steel. No fancy firestriker ferrocerrium rods) Candle lantern for light. No messing about.
All the gear I had was in my blanket roll.
Gotta say...toasty warm.