Jet is a material that adds force to things. Jet puts force on an object, making things speed up or get pushed out of the way. Jet is a "bossy" material that seems to have extra momentum even though it has the same weight and density as every other material.
Jet adds speed to individual Fire particles, causing them to be pushed away from the burning object in a different direction, making the Fire effect look different, and allowing the creation of "lasers". Jet + Hot creates Gubraithian Fire. Liquid Jet (J in Mix Mode) and bulk Mochi creates the Mochi-Jet reaction. Jet makes Powder much more violent and pushy.
Weak Jet with a low jetCoefficient value can be mixed with other elements to make special materials. Weak Jet + Light makes it climb slightly more aggressively. Weak Jet + Rigid makes it push through air and water more strongly without blasting everything out of the way. Weak Liquid Jet pretends to be heavier than Water and sinks, but sits on top of Dense.
Jet adds energy into the OE-Cake simulation, for example by spinning a fan and creating pressure in Gas to move something. Jet can be used with positive or negative values. Occasionally the special properties of negative Jet are useful. Negative Jet still adds energy to the simulation, but in an anti-energy kind of way. The effect of Jet can be extremely non-linear. Positive liquid Jet is hydrophobic, forming droplets and a separate layer just like oil and water in real life. Negative liquid Jet is hydrophilic, dissolving thoroughly but requiring small values or it spazzes out.
Jet is a bit of a cheat to make things move. A natural way to provide thrust on your creations is a Baker Drive.
Jet has "remote force" capabilities. When subjected to an extreme amount of force without being able to move out of the way, Jet particles will apply force outside of their physical location. This causes forcefields to appear around Jet.