The windbreaker’s magic trick is that it has none. What it has is a correct diagnosis of what cold wind actually does.

Wind chill is convective loss

Still air is a decent insulator, and your body warms a thin envelope of it constantly.

Wind strips that envelope away as fast as you build it — that is the chill.

The shell is a wall

A tightly woven fabric stops the air movement at your surface, so the warm envelope survives.

Closed cuffs and a drawcord hem matter because wind hunts for gaps.

The insulation is you

What you wear underneath sets the warmth; the shell only defends it.

That is why the same jacket serves summer evenings and winter touchlines — the layers change, the wall does not.

And the honest limit

No wind, no advantage — a still, cold day wants insulation, not a shell.

A supplier who says so is selling you the right jacket for the right day.