Flak Jacket

Flak jackets are a form of padded protective clothing designed to provide at least partial protection from things such as blunt-force trauma, shrapnel and other projectiles. This can be seen when it protected Iruka Umino from kunai and fūma shuriken during his search for Naruto and the Scroll of Seals. They can also prevent lethal injuries from swords and other weapons as seen during Baki's fight with Hayate. For the most part, they have superseded the plate armour worn by shinobi during the Era of the Warring States and the First Shinobi World War. They are usually worn by chūnin and jōnin over their normal clothing in most villages, although the design varies among the villages and have also changed over time. The jackets are among the most iconic pieces of shinobi equipment. Most of them have pockets or scroll pouches, which can be used to store scrolls, weapons, and supplies. This allows a ninja to access them quickly and/or quietly with only one hand, as seen with Kakashi Hatake's case when he normally does this secretly to extract a kunai.

Trivia

 * In episode 190 of Naruto: Shippūden, Iwagakure genin are seen wearing flak jackets.
 * Several genin in Sunagakure such as Matsuri and Ittetsu have been seen wearing flak jackets. This may be due to the fact that that Sunagakure has a very low population (two out of five stars) but needs to maintain a strong military to maintain its place within the Five Great Shinobi Countries.
 * While flak jackets weren't widely adopted until prior to the Second Shinobi World War, the Gold and Silver Brothers as well as the Second Raikage were seen wearing modern flak jackets during the lifetime of the  Second Hokage (who lived up until the First Shinobi World War).

Styles
Chaleco Táctico