Let's get straight to it — here's what actually matters on this one.

• Merino wool is the standout base layer — naturally insulating, breathable, and much less bulky than synthetic thermal layers.
• Cotton is a poor base-layer choice in cold, active conditions — it absorbs sweat and stays damp, actually cooling you down over time.
• Layer thin, breathable pieces rather than one thick one — trapped air between layers insulates better than a single heavy fabric.
• Wool-blend outer layers breathe better than pure synthetic ones, reducing the clammy feeling common with heavy winter jackets.

The fit-and-fabric-health takeaway: Good winter layering is about trapping warm air near skin without trapping moisture — the wrong base-layer fabric undoes the whole system.

Next up: check out our guide on the fit and fabric guide for wedding season.