During the middle ages basic construction of samurai helmet (kabuto) remained largely unchanged. The bowl (hachi) was of hemispherical form. It was constructed of segments riveted together. At first, there were about 20 segments. Later helmets featured a higher number of them. Bowls of helmets of high-ranking samurai could consist of more than 100 pieces. However, such helmets were not suited for combat since the high number of segments greatly reduced durability. Common samurai used more sensible helmets with bowl consisting of 20-30 segments.
At the top of the helmet was a hole (tehen). Several explanations of its purpose exist. According to the most credible of them, it is quite difficult to rivet all the segments together at the central point of the bowl, while cutting off the points of the segments and thus leaving a hole is a much easier option.
A nape guard (shikoro) was fitted to the backside of the bowl. At first, it was hanging down almost vertically, then it became spreading wider, and by the XIV century the nape guard looked like an umbrella. Then this tendency changed to the opposite, and in Sengoku period shikoro was again almost vertical. Two plates (fukigaeshi) curving backwards were attached to the front of shikoro. Initially they were as tall as shikoro, but later on they became smaller.
Face was protected by masks (mengu), which ranged from those covering only chin and cheeks to covering all face. Sometimes mengu were decorated with imitation of moustache and beard.
About 1550s a new type of helmet appears. Its bowl consisted of only three plates, which allowed making it bulletproof. As the use of firearms became common in Japan around the same time, these helmets became popular even among high-ranking samurai, who otherwise would have shunned such helmets because of their simple construction and cheapness.
Another topic that we have to mention here are decorations of samurai helmets. Perhaps the most iconic of them are antlers. They could take many shapes and were made of various materials. Another kind of decoration was a crest fitted to the front side of bowl. Usually it resembled a crescent or stylised horns, but other, more elaborate designs also existed. Other ways of decorating helmets were too quite numerous. For these purposes lightweight materials like leather, fur, hair, and papier-mâché were typically used, so that the total weight of the helmet won’t increase too drastically.