Golden light does more work than a closet full of down. In cold, clear conditions, low-angle sun loads skin and dark fabrics with shortwave radiation, while calm air keeps convective heat loss in check, turning a frosty street into a quiet personal microclimate.
The real secret is not thickness but trapped still air. Thin base layers hold a boundary layer of air next to the skin; that air has low thermal conductivity, so metabolic heat from steady walking warms it and keeps it in place, as long as wind speed stays modest and fabrics stay dry enough for efficient moisture wicking.
Bulky parkas often overshoot. They encourage sweating, then evaporative cooling kicks in and strips heat faster than the insulation can compensate, especially once a breeze disrupts that boundary layer. Light, breathable layers let walkers match heat production to loss, fine-tuning comfort with zippers, hoods and pace instead of sheer volume.
Time of day quietly decides who shivers. Walkers who head out during calm golden-hour windows stack the odds: higher mean radiant temperature from low sun, less turbulent air, and stable wind chill values, so a thin shell and active muscles can carry the workload that many assume only a heavy parka can handle.