Flak jackets are a form of protective clothing designed to provide protection from such things as blunt-force trauma or even bladed weapons, shrapnel and other projectiles or weaponry. 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, which can be used to store scrolls and also allow a ninja to access them with only one hand, as seen with Kakashi Hatake's case when he normally does this secretly to extract a kunai.
Konohagakure (current): Konohagakure flak jackets are green. They have three scroll pouches on each side of their chest for scrolls, medicine, and other ninja tools. For protection they include a neck guard and extra padding over the shoulders. Newer versions feature pockets. They also have a zipper down the middle. The crest of Uzushiogakure is integrated onto the back of the jacket, symbolising the ties Konoha had with the former village.
Konohagakure (previous): This flak jacket was worn by Konoha shinobi approximately ten years prior to the start of the series as well as in its early stages. It resembles the current one but lack neck guards and pockets.
Konoha ANBU: Konoha's ANBU flak jacket consists of simple reinforced front and back padding with four straps connecting the two pieces.
Iwagakure: Iwagakure flak jackets are brown with only one sleeve on the left arm. They have a large pouch over their stomach or the lower back of the vest. None of these flak jackets hold the presence of neck guards.
Kirigakure: Kirigakure's flak jacket are very basic in design. They are slate grey in colour and pocketless. The most notable feature of these flak jackets are the extended shoulder guards.
Kirigakure (previous): In the anime, a variation on the standard Kiri Flak jacket was seen, with pockets and a neck guard.
Kirigakure ANBU: Kirigakure ANBU flak jackets are also slate grey in colour. They come with or without a neck-guard but have elongated padding over the shoulders, some bearing their village symbol on each padding.
Takigakure: In the anime, Takigakure flak jackets are sky blue. They are otherwise identical to Konoha's flak jackets, minus the Uzushiogakure symbol, although some Taki shinobi do wear metal shoulder-guards attached to their flak jackets.
Benisu Island: In the anime, the flak jackets worn by the shinobi of Benisu Island are beige - roughly the same colour as Suna flak jackets. They have two large pockets on either side of the chest and can be worn over a piece of cloth which hangs down to the wearer's knees.
Land of the Sky: In Naruto Shippūden 2: Bonds, the Land of the Sky flak jackets are purple with two basic pockets on both sides of the chest. They also bear their village symbol integrated onto both of the shoulders.