Warmth is trapped air, not fabric thickness. Below freezing, one enormous coat over a t-shirt loses to three modest layers every time, because each boundary between layers holds a pocket of still, warmed air. The working formula is a wool or thermal base layer against the skin, a proper knit — merino, lambswool or cashmere — over it, and an insulated shell on top. Down gives the most warmth for the least weight; a wool overcoat works too if the knit underneath is doing real work.
Seal the gaps before you add bulk. Most heat escapes at the openings: the collar, the cuffs, the hem. A scarf wrapped so it closes the collar gap adds more warmth than a second jumper. Gloves before your hands hurt, a beanie that covers the ears, and socks in wool rather than cotton — cotton holds sweat against the skin and then chills it. If your core is warm but you're still cold, it is almost always an extremity leaking.
Feet need insulation and grip. Sub-zero pavements mean black ice, so this is the band for lugged rubber soles — leather-soled shoes are a genuine hazard. Boots with room for a thick wool sock beat a tight fit, because compressed insulation stops insulating. If there's slush about, waterproof boots or well-waxed leather; wet feet at 0°C end the day early.
Dress for the walk, not the bus. The classic sub-zero mistake is dressing for the coldest minute of the day and then sweating through every heated interior. Sweat-damp base layers are what make the next stretch outside feel brutal. Favour layers you can actually open or shed — a coat with a full zip, a knit you can take off — and start a long walk slightly cool, because ten minutes of moving will close the gap.
Keep the palette practical. Dark colours absorb what little sun there is, and this weather is hard on clothes: road salt marks leather and hems, so wipe boots down when you get in, and let down and wool dry fully before the wardrobe. Cold, dry air is kind to fabrics — it's the wet interludes that do the damage.
