The Cold is not a spirit, but a validium-based weapon which exists on the border between the Universes; the screaming faces on its skin are images from the other side of the rifts. The Cold is not Highest Entropy Matter, matter that requires vast amounts of energy input just for basic particle interaction to begin. HEM is harvested from the end of the Universe by nechronomancers, who are regarded as pariahs within House society for their belief that past and future do not exist in any significant sense.
HEM isn't the same thing as Cold. In INTERFERENCE, Cold is the substance which forms the heart of Anathema's weapons system: it acts as a kind of buffer between normal-space and Yssgaroth-space, so when the weapon's activated everything in the vicinity vanishes into a great big Yssgaroth-infested hole. To the naked eye Cold looks like a membrane full of eyes, mouths, teeth and animal parts, but by contrast HEM is the energy-proof substance that's draped around the hole to stop any of the Yssgaroth escaping. It's grey-black, smooth and featureless - c.f. the description of Ordifica - and isn't named anywhere in INTERFERENCE. Unlike Cold it doesn't really *need* a snazzy nickname, since by definition it's the least interesting substance in the universe.
What's worth remembering is that the Remote use whatever materials they can scavenge. It's true that the shadow masks they use in INTERFERENCE are made of Cold, but the BOOK OF THE WAR entry on the masks suggests that their form changes between Remote generations… so the lightweight version used in Anathema (Cold) doesn't resemble the military version used by the later Remote on Dust (the same kind described in the BOOK, i.e. almost certainly HEM).
~~~ - Lawrence Miles (from Faction Overload forum response)
The Remote were given the task of freeing the Cold by the Faction, little realising what its purpose was.
Uses for Cold
As an interface substance, most effects of the Cold are based on dimensional movement.
The Remote use the skin of the Cold for armour. Contained in fields to prevent it from eating them. Due to its transdimensional nature, the armour is effectively invulnerable and may only be penetrated at joints, or if the containing fields are collapsed.