First of all, we should mention the fact that types of Japanese armour were quite numerous, and some of them differed from other ones only very slightly. All the types, however, had their names. Here, we shall tell only about the basic types of armour.
In the Heian period Japanese warriors used lammelar armour – more complex o-yoroi (“large armour”) and simpler do-maru (“torso round”). The scales were laced and the lacing was rather rigid – parts of the armour were almost like inflexible plates. At first, do-maru was considered an armour for a common warrior. It was more convenient (for example, a warrior could put do-maru on by himself, contrary to o-yoroi) and its production required less effort (and therefore do-maru’s cost was far less than that of o-yoroi). Both types of armour included tassets (kusazuri). The only defence for arms were sode (shoulder guards) which were of rectangular form and quite large. As the chief samurai’s weapon of the period was bow, armour was optimized for shooting from horseback. As time passed, do-maru replaced the less convenient o-yoroi. The later armour type was still regarded as more prestigious, especially suits made in Heian period and preserved as family heirlooms. Nevertheless, o-yoroi consequently fell out of use in actual battle.
As shooting became less important and samurai tended to fight hand-to-hand, pieces of armour defening arms and legs drastically evolved. A fine example of such evolution are armoured sleeves (kote). At first, only one armoured sleeve was used, and it was the left one. The earliest examples were made of padded cloth, their only purpose was to guard the left arm from the bowstring. Then metallic parts were added, and by the middle of the XIII century two armoured sleeves (for both hands) were in use. The leg defence consisted of suneate (shin guards) and haidate (thigh guards), the later appeared only in the early XIV century.
By the XV century almost all of samurai were wearing do-maru or haramaki-do (“belly-wrap torso” – it was almost identical to do-maru). The scales grew smaller, which greatly improved the armour’s appearance but worsened its protective qualities. At the beginning of the XVI century a new type of armour appeared. It was called Mogami-do (after the region where it appeared). It consisted of horizontal plates rather then scales, but on the outside, through careful imitation, it looked like earlier lamellar armours. Mogami-do was more sturdy than lamellar armours, but it was less popular among the more wealthy samurai.
In the middle of the XVI century yet another type of armour appears – okegawa-do (“tub-sided cuirass”). It also consisted of horizontal plates, but they were riveted, rather then laced, and its surface was plain. Another type of armour – sendai-do (as the mentioned before mogami-do, it was named after the region where it appeared) – too consisted of plates, but they were laminated horisontally. Yet another type of Sengoku period armour was hotoke-do (“Budda’s torso”), which was firstly a smoothed version of okegawa-do, and later it consisted of a single plate. Also existed an armour with frontal plate hammered in shape of a Buddist monk’s torso – Nio-do.
Some scholars speculate that Japanese armours of solid plates were a product of European influence. This opinion is a matter of discussions. However, in Japan actually existed (and some of them still exist now) suits of armour based on European cuirasses. Such armour was called Nanban-do, which means “Armour of southern barbarians”.