

The Repulsion and Propulsion Gels are two of the paints actually used in that game. There's a texture intended for the Hammer map editor that would indicate swapping your portal gun with the paint gun.ĭuring development, the developers used a paintgun for gels, similar to the student game called Tag: The Power of Paint, in which the player could use a gun to paint the environment. It has never been officially used by Valve, who simply call it "sticky gel" or "stick paint". It is often referred to by the community as "Adhesion Gel". The code for sticky gel is still in the game, although disabled by default, and can be re-enabled with this mod (archived download) that requires an older version of the game. It was later shown by Valve with the effects working in a presentation here. A video of the leftovers (albeit after the effects were removed) can be found here. Because of this, several community map-makers have tried (with varying success) to implement it in their maps. All of the Sticky Gel-related textures and particles remain in the final game. The gel is purple, however it is not known whether this would be the final color. This led to it being cut from the game and eventually replaced by reflection gel in the PeTI update.

While this may sound neat, it proved to be disorienting and cause motion sickness among playtesters.
