caps – or casquettes
– with distinctive short brims, long enough to keep the sun out of a cyclist's eyes but not too long to interrupt field of view, first appeared in the early 20th century. At first they were all-white, but as soon as logos were added fans started collecting them. They seem to have gone in and out of style ever since.
Eddy Merckx always wore his with an extra dash of style. Sean Kelly pioneered the poofy-top hat look with maximum "luft." That extra air was supposed to insulate and warm the rider's head — but let's be honest: it was just to look extra-boss.
In the '80s, bike messengers embraced caps and they leaked into street and popular culture, even hi-fashion. Caps became the most iconic cycling accessory. And it became permissible, even dare we say fashionable, to wear them off-the-bike.