Jimbei is mainly a men's summer cloth in Japan. It's made of well breathing cotton and consists a set of pants and a coat. It has usually no obi, and it has been a tied from sides with small strings.
A sides of it you can see only a string and in armpits there is nothing there, therefore it's really cool to wear.
Men mostly wear jimbei for hanabi, a Japanese fireworks show, or omatsuri, a Japanese festival, while girls are wearing their yukatas.
This is one.