From Halopedia, the Halo wiki
Protective and healing armour
- Meduz 'Ra'ashai: "You must first grow your Sanctum's Hide. And not on your armor or skinsuit. It must grow directly on your flesh."
- Thel 'Vadam: "What do you mean, grow? Like scales?"
- 'Ra'ashai: "Perhaps grow is the wrong word. Accumulate might be better. It gathers on your flesh, like dirt, and cannot be washed off. Soon, you are coated in it, and it is your armor. When that happens, the Blessing comes. The Sanctum responds to your desires."
- — Blademaster Meduz 'Ra'ashai and Arbiter Thel 'Vadam discussing Sanctum's Hide.
Sanctum's Hide is a thin cloth-like material used as armour by the Defenders of the Sanctum, the inhabitants of the Sanctum of the Ancients on Netherop. The armour-like material is formed thanks to the presence of Precursor nanotechnology in the Sanctum, and is formed thanks to years of exposure to the dust during the Defenders' long tenure residing on the planet.
Named as such by the Defenders of the Sanctum, Sanctum's Hide is as tough as graphene, as light as air, self-cleaning, self-repairing, and automatically forms on the body of those who inhabit the sanctum for prolonged periods of time. The hide is formed from Precursor nanotechnology found inside the sanctum, which grows on the skin of the sanctum's inhabitants until they are covered in a thin layer of the substance. While it does not provide energy shielding or strength enhancement like MJOLNIR Powered Assault Armor or fighting skins, the hide is highly resistant to physical attacks.
Visually, Sanctum's Hide resembles a grey shimmering, cloth-like material. When worn by the Sangheili Defenders of the Sanctum, the form-fitting material covered the troops' heads to resemble clear masks, with shimmering formfitting guards for their mandibles.
However, it can be used to provide a limited form of active camouflage if the wearer wills it. This camouflage may be broken, however, if another person inside the sanctum and similarly-commanding the sanctum's nanotechnology knows what signs to look for. Corresponding with the Sangheili Expectation Effect theory, if a person expects to see someone hidden by Sanctum Hide's camouflage, then the camouflage will be revealed. This active camouflage is susceptible to thermal imaging.
The same processes that form Sanctum's Hide can be used to heal a given wearer, and even regrow limbs - as in the case of the Ranger Klemas 'Teodoree, who had lost a leg during the Battle of Netherop and had a replacement regrown of Sanctum's Hide.
When a wearer of Sanctum's Hide dies, the nanotechnology dissipates and the hide "dies" with them. Following the removal of the Divine Hand from the sanctum, the Sanctum's Hide protecting Nizat 'Kvarosee and Tam 'Lakosee began to slough off and die, corresponding with a similar die-off of the fruits and purified water in the sanctum. However, this may have also been because both Sangheili were dying of infections, hunger and thirst. Tam believed the ongoing loss of their Sanctum's Hide was a sure sign that they were both dying. 
List of appearances
- Halo: Outcasts (First appearance)