Astral conduit

Astral conduits are tunnels which stretch through the void of the Astral Plane, connecting the Prime to the Outer Planes. It is through these that the belief and faith of mortals travels to their powers, that the spirits of the dead journey through to their ultimate destination, and which the powers use to grant their followers their spells. Conduits can also be used for normal, "physical" travel, bringing a person from one end to the other in less than a second just as a normal portal. Conduits are by far the safest means of planar travel; though they do have their own dangers (such as the h'rak'va or the rumored conduit cleaver), mishaps relating to a conduit are few and far between.

The average conduit has a diameter of almost 10 feet, and has been described by others as feeling like "both a tingling energy construct and some very smooth, membranous tube". A very few substances are able to affect a conduit from without, and there is no way yet possible to affect one from within. Conduits are fairly restless things, whipping about whenever in use. There's a definite danger of striking a poor, hapless bystander when it happens, and thus most folks recommend staying far from conduits whenever possible.

When an astral conduit is born, it tends to suck a large amount of matter in from both sides; this is the source of most of the astral islands drifting about today. From its creation, the average conduit has a life span of about 1,000 years, passing through three stages of development.

• Young: Lasts from birth to about 200-300 years. One-way, with a tendency to move about, changing origin and destination with variable frequency.
• Mature: Lasts for approximately a further 400-600 years following the Young stage. Two-way, with relatively fixed endpoints, rarely if ever moving. Rarely suffers a burst, causing the conduit to rupture somewhere along its length, and dump travelers into the Astral itself.
• Old: Lasts until the death of the conduit, usually 100-400 years following the Mature stage. Shifts between one-way and two-way seemingly at random, with endpoints even more unstable than young conduits, the far end even often jumping between whole planes.

In most cases, the death of a conduit is preceded for some time by a phenomenon known as "fluttering", where the conduit begins to jump in and out of existence. This state can continue for days, until finally, it fades entirely. This can be a potentially risky time to use a conduit, as the fate of a cutter stuck inside a conduit when it jumps out of existence is as of yet entirely unknown.

A conduit which is irreparably harmed in some manner, however (most often due to either a conduit cleaver or a burst) instead withers, the two disparate ends shriveling up and eventually dissolving into the void.

Note that despite the terminology used here, there is no proof either way as to whether or not conduits truly are alive. Though it could be the case, none have ever been able to definitely confirm one way or another; a third theory is that conduits are in fact all part of one much larger being, filling the Astral.

The silver cord of an astrally projected traveler is in fact nothing more than an artificial conduit, a manifestation of the astral spell created long ago to establish a link between the astral traveler and their physical body. Given the effect of silver swords on astral cords, most assume they are similarly effective against conduits, even if few githyanki would attempt such a thing.

Reference

• A Guide to the Astral Plane, pp.24-29