Phlogiston

Phlogiston, more commonly called the Flow or the Rainbow Ocean, is a multicolored flow of ether that connects together most of the crystal spheres floating in the Astral Sea. Phlogiston currents are utilized by spelljamming vessels to travel between crystal spheres.

Properties

Phlogiston is extremely flammable, and an open flame will ignite all the phlogiston in the immediate area to burst into flame. Because of this, nearly all spelljamming ships either douse all flames upon entering the Flow or take great pains to prevent the Flow from contacting with the fires they do have.
Thankfully, fire isn't needed to see while sailing in the Astral Sea, as phlogiston is luminoious, generally resembling a mixture of orange, white, reds, and light blues. However, lower deck areas of ships are generally reliant on nonflammable, natural lighting, such as flourescent moss, various magical items, and so on, as the Flow doesn't usually infiltrate the entirity of a ship.
Unlike Wildspace, where temperatures outside of the air envelope of a spelljammer are sub zero, resulting in a quick, frozen death, the Flow is generally pleasant, often compared to a cool summers day. However, few experience this naturally, as the Flow has a preserving effect on living creatures that end up floating insdie of it that aren't adapted to its nature.
Travellers that fall or are tossed into a phlogiston current end up in a form of suspended animation, falling into a deep torpor as their skin hardens and becomes gray, their bodies functionally calcifying. A living creature preserved in this way can be revived when placed inside of the air envelope of a spelljammer or in a planet's atmosphere. While creatures are functionally immortal while preserved this way, they also tend to suffer terribly from being deprived of their senses for so long. Phlogiston preserved humanoids are at great risk of of becoming survivors, who attempt to regain their sense of feeling by possessing and dominating those around them, or becoming a flowfiend, either by their own evil nature warping them or being corrupted by an already existing fiend.
Finally, the presence of the Flow interferes with extra-dimensional magic and spells. This means that transdimensional spells, such as Banishment or Plane Shift, cannot send a creature to or out of the Flow. Additionally, the Flow prevents the summoning of creatures from different planes. Phlogiston also interferes with spells and magic items that create pocket dimensions, such as bags of holding, also stop functioning. For bags of holding in particular, the contents of the bag are expelled from its dimension while in the Flow.
Because of all of these properties, and the connection the Flow shares between the crystal spheres, it has been hypothesized that the Flow is a gaseous form of the Material Plane that floats through the Astral Sea.

Localization

While found all throughout the Astral Sea, the Flow only appears to connect crystal spheres with one another. Phlogiston generally cannot enter into a crystal hphere, and any attempt to bottle it and bring it into Wildspace results in the phlogiston dissipating. One known exception is Crackedspace, but due to the destroyed nature of the sphere, the wildspace inside of its remnants is functionally identical to the greater Astral Sea. Crackedspace is also considered extremely dangerous, as the Flow will eventually seep far enough into Wildspace to come into contact with the system's sun, igniting all of the phlogiston in the sphere in a massive, destructive inferno.

A representation of the colors usually found in the Flow

Type

Metaphysical, Astral