The phlogiston (flōˈjistən) is a turbulent, unstable, multicolored, fluorescent gas (or gaslike medium) which fills the regions between the crystal spheres. Very little is known for certain about the phlogiston or this region. Every planetary system known is encased with a crystal sphere, which floats in the phlogiston, very slowly bobbing up and down over time. Essentially, the crystal sphere keeps the Wildspace in and the phlogiston out – phlogiston cannot be brought into a crystal sphere by any known means.
Travel between crystal spheres is enabled by "Flow Rivers" – sections of the phlogiston which have a current and greatly reduce travel time. Travel through in the "slow flow" (off the Flow Rivers) is possible, but very dangerous.
The phlogiston reacts explosively to all magical and non-magical sources of fire. Unless one is resistance or immune to fire, it is strongly recommended not to cast or produce a flame in phlogiston unless one wishes to burn to death and cause the complete destruction of their vessel.