Armor

Body parts

Armor can cover the entire body, or just part of it. Here is a list of body parts and armor parts that cover them. As you can see, English armor vocabulary is heavily influenced by French.
Not every body part is considered equally important, so each has been given a rating. The total for all body parts combined is 100%.

Helmet

Because the head is such a vital part of the body, helmets deserve some extra attention. They come in a wide range of shapes. All helmets are a compromise between protection and freedom (sight, hearing, breathing, weight, moving the head), trading one for the other. In the list below, helmet models are roughly categorized in order of increasing protection. Note that some helmets include throat/neck protection, which is not taken into account in the list, but of course does add additional protection. The focus is on battlefield helmets, not tournament models, which tend to be heavier and bulkier.

• Skull cap: Covers only the upper part of the skull. Examples: skull cap, kettle helm, Japanese kabuto.
• Open helmet: Skull cap with additional protections like nose guard, face mask, and/or cheek guards. Examples: (classical) Illyrian helm, Chaldician helm, Attican helm, Roman helmets; (medieval) spangenhelm, nasal helm, burgonet.
• Half-open helmet: Covers the entire head but leaves a T- or Y-shaped area in the face open for seeing and breathing. Examples: (classical) Korinthian helm; (medieval) barbute.
• Closed helmet: Covers the entire head. Usually equipped with a moveable visor. Examples: close helm, bascinet / hounskull, armet.

Materials

Early armor was made of cloth or leather. These were quickly surpassed by metals. But soft armor remained in use as material for undercoats, to protect less vital areas like limbs, or the whole body if money was short supply. Early metal armor was made of copper, a relatively soft metal that was easy to work. Copper was quickly supplanted by the tougher bronze, usually in a mix of up to 88% - 90% copper and 10% - 12% tin, called "classic" bronze. The next revolution was iron working, which required an entirely different smithing process at much higher temperatures. Early iron was of low quality, but less scarce than the tin needed to produce bronze. The final step was to transform iron into steel, making it much harder. Smiths gradually improved their methods of making wrought iron (too little carbon content) and cast iron (too mach carbon) into steel (just enough carbon). Ancient and medieval steel was better than bronze, but still less than the best factory-produced modern steel. In the meanwhile, some societies which lacked a sufficient source of metals used materials like horn or wood. The Chinese even invented paper armor, which is suprisingly effective and lightweight, but not durable.
The table below lists effective properties for common (and some uncommon) armor crafting materials. The data given for paper, cloth and leather is not for a single layer, but a padding of several layers.

Construction types

Here is a list of different types of armor, more or less in chronological order of development. All metal armors require some kind of undercoat to protect the skin from chafing and this is considered to be part of the armor.

Cloth	All cloth armor consists of several layers of cloth made of linen, wool or cotton, which are quilted together. It can be worn as an undercoat for heavier armor or as an independent armor itself. The former is called aketon, arming doublet or several other names; the latter is named gambeson, though the names are often mixed up. The standalone variant is specialized, much thicker, especially in places where protection matters the most. Cloth is always composed of several layers, from just a few up to 20 - 30. As armor, it has limitations, but is cheap and quite effective in some aspects.
Leather	Leather is animal hide, hardened by tanning. It is sometimesused as undercoat for other types of armor, but also standalone. Most common are tanned and waxed leather which are much more water-resistant than untreated leather. Another variant is leather that is hardened by boiling in oil, becoming "cuir bouilli". This is harder but also more brittle than normal tanned leather. Similiar to cuir bouilli is leather that is lacquered, a technique that was mainly used in Asia. Like cloth, leather armor usually is a padding of several layers.
Scale	Scale armor is made from studs (called scales) that are attached to both each other and the undercoat. The scales are often triangular or U-shaped, and overlap each other from top to bottom. They can be made of iron, steel, bronze, brass, horn, leather (raw, waxed or lacquered) or even animal shells. The result looks like the skin of a fish, hence the name 'scale' armor. It is also called 'leaf' armor. An example is the Roman lorica squamata. Scale armor is known since ancient times but was largely supplanted by lamellar and mail, which offer better protection for the same weight. Yet scale armor was not totally obsoleted, as it breathes well and is almost as flexible as mail.
Lamellar	Like scale armor, lamellar armor is made of studs (called lamellae). The difference is that they are only connected to each other, not to the undercoat. Also, their shape is often simply rectangular. They can partially overlap like scales, usually upward instead of downward, or be aligned next to each other. The material for the lamellae is usually iron or steel, but is as varied as the scales of scale armor. Lamellar armor takes more effort to construct than scale, but is generally easy to maintain. It can be worn as indepent armor or over a secondary layer, for instance mail. In most lamellar armors, the lamellae are laced together with strings. These are somewhat vulnerable to damage, but easy to repair, even in the field by a common soldier. Another method is riveting them together, creating a tighter and sturdier whole. The more the studs overlap, the better the protection, but worse the airflow, flexibility and maintenance. The origin of lamellar armor is ancient and it has remained popular in Asia for millennia.
Splint	Splint armor resembles brigandine, but here the studs are expanded into strips. The most common method of assembly is riveting them into the undercoat, without any outer layer, like brigandine armor. It is most commonly used to protect the lower arms and legs, where strips are aligned with the limbs. Splints can be positioned close together for good protection, or with some space in between for more flexibility.
Laminar	This type of armor consists of (usually horizontal) bands that overlap each other. They are connected by a combination of straps and riveting. Another name is 'banded' armor. The Roman lorica segmentata is an example with relatively loose fitted bands. Laminar armor was largely superseded by plated mail when that type of armor was introduced.
Mail	Mail is often named 'chain mail', though that name is a Victorian invention. 'Mail' is the official term. It consists of interlocking metal rings. Mail protects well against cuts, but is weak in protecting the head and joints. However combined with padding underneath it protects the wearer quite well. Also it is very flexible to wear and move in, and can be cleaned easily by rolling it around in a bag filled with sand. These qualities have made it the most popular type of armor in history. The protection offered by mail depends very much on the material, the weave density and ring thickness and also upon the type of construction: riveted is better than welded is better than butted. Almost all historical mail is riveted. It is best supplemented with a thick undercoat to protect against thrusting and crushing attacks. A "byrnie" is a waist-length mail shirt, a "haubergon" reaches down to mid-thigh and a "hauberk" down to the knees. Mail may also be extended upwards with the addition of a "coif" to protect the head, though usually a proper helm is worn over that.
Coat of plates	This type consists of medium sized metal plates that are sewn onto an undercoat. It is an intermediate type of construction from the small scales, lamellae and rings of earlier armor types to full plate armor. Coat of plates is often confused with brigandine, but its plates are larger and the method of attaching them to the undercoat differs. It is the somewhat more primitive forerunner of brigandine.
Brigandine	Brigandine armor consists of small to medium metal plates riveted into an undercoat, sometimes under an outer layer of leather. The studs can be adjacent or overlapping. It is often labeled as the poor man's plate armor, though more flexible and quite effective overall. The name brigandine derives from brigand and is often confused with its modern equivalent of bandit, but brigand originally meant footsoldier, which is where the association comes from.
Plated mail	As the name denotes, this type is a mix between plate and mail. It is not a suit of armor where some parts are plate and others mail, but rather medium sized plates joined together by mail all over. The plates can be adjacent like in lamellar armor, or overlap like in laminar. This type is popular in Eastern Europe and the Middle East.
Plate	Plate armor is made up from large plates, "lames", all custom made to fit specific parts of the body. The plates are linked together by rivets and straps. If well-crafted it is superior to all other types. Average thickness of plate varies from 1 mm (limbs) through 2 mm (cuirass) and 3 mm (helmet). A Renaissance bullet-proof cuirass could be even thicker, in places some 4 mm or evene more. Plate uses less material and can be made in less time than mail, however it requires relative advanced steel late medieval smithing technology to be able to craft large lames. A full suit must be made to fit the wearer snugly and this requires a very skilled smith. Thus it is more expensive than other armor types. Simpler plate armor variants like 'munitions' armor exist too, not covering the entire body and using inferior steel. These are less effective but cheaper, suitable for mass production.

Armor type table

The table below gives a rough categorization of the pros and cons of different types of armor. Legenda for appliance: + = very suitable, ~ = somewhat suitable, - = unsuitable.

Use in roleplaying games

In combat without firearms or magic, but just plain old melee and missile weapons, armor is a vital part of defense. It does not make you less likely to be hit, like Dungeons & Dragons states, but instead absorps impact energy, decreasing wounds. The price that the armored warrior pays is encumbrance and hampered senses. But how much?
Using the data listed above, you can build many different armor "systems". Players who want detail should go for "piecemeal armor", where different parts of the body are protected by different pieces of armor. Attacks should be directed at those specific parts of the body and the type of attack (thrust / slash / crush) should be specified too. You can calculate the protection value of the armor by multiplying: construction type x material x thickness x quality. Similar formulas can be set up for other attributes like weight, freedom of movement, loudness, hampering of the senses and cost.
If you do not want so much detail, you can calculate an overall armor score by rating the whole as the weighted average of the parts. For instance: This value 8 helmet combined with this value 6 cuirass, which also covers the shoulders, without any other protection, has a total value of ((8 x 20%) + (6 x (25% + 15%)) / 100% = 1.78, rounded to 2.
If even that is too much work, you can use predefined sets of armor and have each rated at a fixed value. For instance: This humble scale cuirass has an armor rating of 2, while this splendid royal suit of plate armor rates at 9.

References

• Good introduction: http://www.medievalwarfare.info/armour.htm
• The museum of the Salish has a nice introduction on armor: http://www.temixwten.net/biblio/IQP-EvolutionOfMaterials-MedievalEra.pdf.
• Replicas, reviews, articles and discussions on medieval armor and weapons can be found at https://www.myarmoury.com/.
• Matthew Amt has a nice collection of information and hyperlinks about ancient Greek hoplites, including their armor, at https://www.larp.com/hoplite/index.html.
• This: http://www.steamfantasy.it/blog/2008/02/23/le-armature-una-panoramica-degli-acciai/ Italian website has good numbers on hardness and penetration tests.