Reflective, high-viz gilet

[Zen]

for further confusion value, a vest in the UK is what you wear under your shirt in winter to keep you from catching a cold!

We just call that an undershirt

What I can't figure out is why a sweater is called a jumper.
Which begs the question "Does a sweater make you sweat?"
Well, sometimes but a sweat suit is what one wears when one intentionally expects to sweat.

A jumper is a type of girls dress here