One of the most important rules of personal combat is – if you are going to draw that pistol, better wear armour. Other important rules include 'avoid detection', 'avoid getting hit', and 'always carry a bigger gun than the other guy'. But if you make combat a habit then sooner or later you will get hit, and without body armour chances are you'll be very dead very quickly. Although the old saying 'a bullet in the head will make you very dead, but a bullet in the arm does very little harm' is still true, there are many weapons on the 40k battlefield that can kill you with even a glancing hit – 'a bolt shell in the head will blow it apart, and a hit to the arm will kill you nonetheless'. So be a good boy and wear your armour.

Note that having a tough armour will protect you from damage from weapons, but it does not necessarily protect you from everything else. Armour therefore frequently comes with several additional protective options; many of these are only available for completely sealed suits, or for those wearing a helmet/hood with their armour. Options include climate control, respirators, rebreathers, air supply, photovisor, hearing protection, radiation protection, pressurization, sealed, vacuum support. It's also possible to integrate various other systems in armour; sensors, weapons, power supply.

Primitive armour: Primitive armour is similar to primitive melee weapons; it's used by those who do not have access to modern equipment. The primary users are warriors from primitive words, but you'd be surprised by the number of hive gangers and others found using it. Various leathers and hides are primitive armour, as are purpose-crafted chain mail and plate armour, as well as more hi-tech but improvised materials – for example unarmored space-suits, furnace worker smocks, and steel-plate armoured industrial exoskeleton.

Flak: Flak armour is the most commonly seen armour type in the Imperium. It consists of multiple layers of ballistic ('flak') weave that is designed to deflect and dissipate incoming energy. It is quite effective against projectile weapons, concussion and fragmentation, but is next to useless against high-powered energy weapons or bolters.

The Imperial Guard (and many PDF forces) are equipped with flak armour. Such armour is normally not sealed, although by adding an auxiliary breathing mask and gloves a similar effect can be achieved (for a limited time period at least). Many Guard units augment their flak armour with carapace reinforcing segments; a hi-threath helmet is nearly ubiquitous, but many (Stormtrooper regiments in particular) also wear carapace chest-plates and so on. Many security troopers and enforcers also wear flak armour, usually flak vests.

Mesh: Mesh armour is one step up from flak armour; the basic design is the same, but the armour is interwoven with strands of carbon nanotubes. Mesh armour gets its name from the faint geometric designs found in many such armours; testament to the various weaving techniques used. When mesh armour is damage it can be repaired by replacing the damaged segments only. When struck by incoming fire mesh armour will become rigid and prevent impact trauma damage to the wearer and will also effectively dissipate directed energy.

Mesh armour is not as widely used in the Imperium as flak armour; only the Mechanicus and certain tech-guilds know how to make it. As a result mesh is too expensive for widespread use with military forces, except among some Special Forces Regiments. It is, however, the preferred armour of those with resources; the armsmen of an ancient noble family, the security guards of a major business venture, or the heavy muscle of a top kingpin.

Crysweave: Crysweave, or mono-crystal diamonid nanofibre as it is sometimes called, is the ultimate ballistic armour found within the borders of the Imperium. The resultant armoured suit is both light and flexible, while retaining superbly good protection characteristics against both projectile and energy weapons.

Crysweave is rare and expensive. It is manufactured only by a select few Forge Worlds and sold only to the Imperium or certain select clients. It is rumoured that certain elite assault units within the Tech-guard are equipped with this type of armour. Imperial Temple Assassins also come equipped with cameleoline crysweave armour. Other users include security-conscious nobles, senior adepts and Rogue Traders; men who need protection but cannot dress up in full battle-armour.

Carapace: The so-called carapace armour is made of interlocking armour plates worn over a flexible backing. That's the common denominator, from which many variations can be made. The carapace armour is either made of single parts – such a the light infantry helmet worn by the Imperial Guard and others, or the clamshell breast-piece worn by some front-line assault units – or is part of a full suit of hard-shell sealed combat armour.

The plates themselves are a sandwich of hi-tech composite materials designed to provide optimum protection form a variety of weapons. The most basic types combine typically combine and inner layer of woven ballistic fibre and and outer ablative layer of ceramite, over a core of plasteel. The resulting armour offers excellent protection from all common weapons found on the 41^st Millennium battlefield. For those who can afford it and have the connections the Mechanicus can provide more advanced materials technology; mono-bond crystal weave, collapsed matter hardening, and refraction ablation to name a few. Ultimately it is possible to create carapace armour using power field projection techniques; in effect creating an armour that creates it's own internal stasis effect – the exact opposite of entropic effect found in the annihilation field of a power weapon.

Power armour: Power armour is the ultimate form of personal protection. In essence it is just a suit of sealed heavy carapace. A suit so heavy that it requires its own internal power supply and locomotive system to operate. Because of this power/locomotion arrangement armour protection can be increased without slowing the wearer down, and also allows the wearer to employ much heavier weaponry than an unaugmented human could. In practice all power armour suits will come equipped with a full range of auxiliary systems as well.

The end result is a hideously complex and expensive piece of equipment that requires years of training to use correctly. But that piece of equipment turns the wearer into a light armoured vehicle capable of replicating the full range of human movement and employing weapons of sufficient power to deal with any battlefield threat. That said there are many variations of power armour; raging from primitive versions that are little more than armoured exoskeletons, via 'civilian' versions of intermediate sophistication, to the Mechanicus-crafted masterpieces of techno-arcana worn by the Adeptus Astatres – the Angles of Death – and the Adeptus Sororitas – the Emperor's Handmaidens.

Terminator armour: Terminator armour is a special form of heavy assault power armour employed by the Adeptus Astartes (in very limited numbers) and a few choice Throne agents. Superbly well armoured using the finest Mechanicus armour technology the Terminator suits are intended for short range action against entrenchment and well-equipped enemies. The added power of Terminator armour allows them to field weapons even more potent than those used by normal Marines; rapid-fire storm bolters and assault cannon for the most part. Terminator suits lack the auxiliary backpack of normal power armour; all systems are carried internally for maximum protection. The lack of a jump pack, lower ground speed and limited motion range means that Terminators lack the mobility of power armoured Marines. To compensate all Terminator suits are equipped with teleporter beacons; it sis standard procedure for Terminator suits to be inserted and extracted by teleportarium.

Dreadnought armour: Dreadnought combat suits are more correctly classified as walking tanks; such is their level of protection and firepower. The operator sits deep within the chest cavity of the armour, protected by multiple layers of heavy armour. Linked directly into his armour the operator has an unique ability to perceive the battlefield, without actually sensing it directly. Dreadnought armour utilizes advanced armour components and is capable of withstanding most hand-held weapons; the use of anti-tank weaponry is recommended. Dreadnoughts frequently carry multiple heavy weapons; hi-power lascannon, autocannon, plasma cannon and hi-focus melta weapons.