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. For the most part, they have superseded the plate armour worn by shinobi during the Era of the Warring States and the First Shinobi World War.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, 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 pockets and sometimes neck guards as is the case with Dan Katō's.
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 features of these flak jackets are the extended shoulder guards and a lower extension to protect the lower abdomen.
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.
Kumogakure (previous): This flak jacket was worn by Kumogakure shinobi approximately ten years prior to the start of the series. Unlike the current style it had extra shoulder, neck padding, and a scroll pouch.
Takigakure: In the anime, Takigakure flak jackets are sky blue. They are otherwise identical to Sunagakure's flak jackets, minus the scroll pouches, neck guard, and shoulder padding. Additionally, some Taki shinobi do wear metal shoulder-guards attached to their flak jackets while others opt for pockets.
Hoshigakure: In the anime, Hoshigakure flak jackets are blue. They have two scroll pouches near the hip and are held together by three straps by the neck-guard.
Jōmae Village: In the anime, the Jōmae Village's flak jackets are brown. They have no sleeves and appear to be completely plain. Other than that, they come with a throat guard and come with shin guards.
Prajñā Group: Flak jacket worn by these shinobi are dark green. Other than that, they resemble Konohagakure's flak jackets; minus the Uzushiogakure crest and the scroll pouches. Instead, they opt for a back pouch similar to Iwagakure's.
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 and have a flap beneath to protect the lower abdomen. They also bear their village symbol integrated onto both of the shoulders.