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 and was ambushed by Mizuki. They can also prevent lethal injuries from swords and other weapons as seen during Baki's fight with Hayate Gekkō. For the most part, they have superseded the plate armour widely used by shinobi during the Era of the Warring States and the First Shinobi World War.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.
Several genin in Sunagakure such as Matsuri and Ittetsu have been seen wearing a variant of their village's standard flak jackets in the manga, items which are usually given to shinobi of chūnin rank or higher.
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 (which is fastened on by steel buttons). They also have a zip 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 (movie variant): In Naruto Shippūden 4: The Lost Tower, Minato's team was seen wearing a unique flak jacket. They are dull brown and came with angular shoulder guards, a throat guard, a neck guard, and one scroll pouch attached to the left shoulder. It is possible that this was merely an experimental model as it hasn't been seen prior to or after the Third Shinobi World War.
Konohagakure (wartime variant): Worn during the Second Shinobi World War, this flack jacket consists of a steel grey over-vest worn over Konohagakure's first generation flack jacket. It was connected by straps over the shoulders and hips. It also came with protruding shoulder guards, extensions to protect the lower throat and abdomen, and steel gauntlets.
Konohagakure (previous): This flak jacket was worn by Konoha shinobi approximately ten years prior to the start of the series during the Second Shinobi World War. It resembles the current one but lack pockets and sometimes neck guards as is the case with Dan Katō's. The lack of scroll pouches was remedied by wearing two additional equipment pouches on the lower back instead of one (as is the case in modern times).
Konoha ANBU: Konoha's ANBU flak jacket is steel grey and come with steel gauntlets and seem to be connected with a interwoven band near the stomach along with a zip. They also come a sword mounted on the back just over the right shoulder by a metal holster.
Sunagakure: Sunagakure flak jackets are beige. They may or may not include shoulder padding, shoulder guards, neck guards, and scroll pouches over their stomachs. They all however are fastened by a zip in the front and by metal clasps on the shoulders. They also come with some kind of pouch in the lower back.
Sunagakure (variant): Another flak jacket model has been seen being worn by several genin-level shinobi from Sunagakure. It is brownish-beige, is fastened by a zip, and lacks scroll pouches and reinforced shoulder padding. However, this is compensated by having a neck guard that envelopes the entire neck and segmented steel arm-guards.
Iwagakure (current): The current Iwagakure flak jackets are bright brown and look exactly like the old version, but instead of brown cloth, red is used in the uniform. Also, the pouches and the connecting strap are now brown rather than grey like the previous generation.
Iwagakure (previous): The old Iwagakure flak jackets are dark brown with only one sleeve on the left arm. They have a large grey pouch over their stomach and another over the lower back of the vest. Both pouches are fastened on by a grey strap over the stomach. None of these flak jackets hold the presence of neck guards though they do retain shoulder padding held in place by buttons and zip that go down the middle.
Kirigakure (current): 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 lower extensions on either side to protect the lower abdomen. Unlike the majority of the styles used (which use zip) this flak jacket was fastened from the sides by straps.
Kirigakure (previous): In the anime, a variation on the standard Kiri flak jacket was seen. Unlike its counterparts, it came with two scroll pouches on the lower left side, a pocket on the right chest, a built-in pouch on the lower back, a neck guard and is fastened by a covered zipper. The village's symbol is also embedded on the back. However, there is also minimal padding on the sides.
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. Like the flack jacket used by the Kirigakure's regular forces, it is held together with straps from the sides.
Kumogakure (current): Kumogakure flak jackets are white. They have a rather utilitarian version with no scroll pouches and only one strap over the left shoulder to hold it in place. The strap is attached via a button and the jacket has a strange design on the front which consists of one diagonal line going down to the left with four small lines on top and one medium size line line going down to the right that is perpendicular the previous line.
Kumogakure (previous): This flak jacket is dark grey and 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, mesh armour near the collarbone, three scroll pouches on the chest, and is fastened by metal clasps on the right side (though some don't have scroll pouches or mesh armour as is the case with the Kumo spectators).
Otogakure: Otogakure flak jackets are black. For protection, they come with shoulder padding (which is fastened on by steel buttons) and a neck guard. They are also fastened by three metal clasps on the left side and have a pouch in the front just over the stomach.
Takigakure (current): In the anime, Takigakure flak jackets are blue. They are otherwise identical to Sunagakure's flak jackets, minus the scroll pouches, neck guard, metal shoulder clasps, and shoulder padding. Additionally, some Taki shinobi wear metal shoulder-guards attached to their flak jackets while others opt for two pockets near the stomach like the the ones worn by the Taki Kunoichi.
Takigakure (previous): In the anime, this flak jacket was worn in Takigakure approximately ten years prior to the start of the series on the eve of the Second Shinobi World War. It has thick shoulder padding, a neck guard, extensions on both sides to protect the lower abdomen, one large pocket on the right near the stomach, and is fastened by a zip. However, it left the upper sides of the torso exposed while the lower half was only protected by thin padding.
Hoshigakure: In the anime, Hoshigakure flak jackets are blue. They have two scroll pouches near the left hip and are held together by straps on the right side and by the neck-guard, which surround the entire neck.
Jōmae Village: In the anime, the Jōmae Village's flak jackets are brown, have no sleeves, and appear to be completely plain. Other than that, they come with a throat guard that surrounds the entire neck, shin guards, extend slightly downward to protect the lower stomach, and are attached by straps over the collarbone and hips. They also seem to favour using mesh armour to protect the shoulders.
Moyagakure: In the anime, the flak jacket worn by the shinobi from Moyagakure are beige in colour and had two large pockets on the chest area and two built in pockets at the sides. The shoulder padding is also reinforced and the zip is covered. In addition, they come with elbow and knee-pads.
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, two in the lower sides, extra shoulder padding, and a built in neck guard. In addition, they also have a concave triangular symbol embedded in the back. They are also fastened by a zip and can be worn over a piece of cloth (which also has the same symbol) that hangs down to the wearer's knees.
Prajñā Group: Flak jackets worn by these shinobi are dark green. Other than that, they lack any accessories except for three pouches on the lower back that are fastened by a band. They also posess a zip that runs down the middle, neck guards, and padded shoulder-guards.
Fūma clan: The flak jackets worn by these shinobi are dark blue. They possess extended shoulder guards but no neck guards. They also come with black bands on the side and are fastened over the top with the same type of bands with metal clasps along with a zip. They also come with iron gauntlets and a fūma shuriken holster on the back.
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, are fastened by a covered zip,and have a flap beneath to protect the groin. They also bear their village symbol integrated onto both of the shoulders which is reinforced with additional padding.