Gel

Gel or Paint is a puzzle element of Portal 2. It flows in blobs, or in packets of blobs as bombs, and covers most surfaces or objects it touches, changing the physical properties and coloring it. The exceptions to this are glass and grating: glass cannot be painted, and gel travels through grating. Gel streams can be redirected with portals and excursion funnels.

Types of Gel
There are six gel types:
 * Repulsion gel: Blue, causes things to bounce around.
 * Propulsion gel: Orange, reduces friction, making objects slippery and players move quickly.
 * Conversion gel: White, allows portals to be placed on any surface to which it is applied.
 * Cleansing gel: Clear, erases effects of other gels.
 * Reflection gel: Unused (but mostly functional) gel that reflects lasers. Blob texture and particle systems are missing. Does not properly apply to physics objects, except to negate the effects of sliding on propulsion gel.


 * Adhesion gel: Unused gel that allows players and objects to stick to surfaces. This is non-functional, except for negating the effects of propulsion gel if applied to cubes. The code for this used to exist in Portal 2, prior to the DLC1 update replacing it completely with reflection gel. There have been recreations of this gel with VScript.

Using an instance
Place a entity with the following properties:

If the dropper doesn't show up, try restarting Hammer.

Create the entity you want to activate the gel dropper, such as a at the entrance to the room, and give it the following output:

From scratch

 * 1) Place a dropper prop, including any visible pipes.
 * 2) Place an inside the dropper, and tune it to your liking.
 * 3) If there is anything that enables or disables the gel dropper, send Start and/or Stop inputs to the.
 * 4) Depending on your model, you may want to change skins or play animations when enabled or disabled.

If you want to create paint bombs, follow these steps in place of an :
 * 1) Place a, and give it a name like.
 * 2) Place a . Give it a name like  and set Template 01 to.
 * 3) Place an . Give it a name like  and set Point_template To Spawn to.
 * 4) Put this output in your :

This how Valve does their droppers in Portal 2. Alternatively, you can use a instead using the output above, just change OnExploded to OnTimer. This alternative method will allow multiple paint bombs to be used at once, greatly increasing the chances of two bombs colliding with each other in midair, which will probably be a nuisance.

If your input device can be activated rapidly, consider having a do the spawning inputs so that you can temporarily disallow the   from spawning more paint bombs after your device is activated.

Conversion Gel Color
There is some evidence saying that conversion gel was originally pure white, and that the current gray color was an accident by Valve, made while developing the 6th coop campaign (Art Therapy).

How Valve could have missed this is not very clear, because at least one Art Therapy map used conversion gel, so they must have noticed. It could have been an intentional change, possibly to make it blend in better with darker areas, or so it's more visible on white surfaces.

Whatever the case, you can change it to pure white with this console command:.

Controlling gel
When designing a puzzle, be very mindful of possible exploits that may arise! It is generally very easy to exploit, and it should therefore be handled somewhat restrictively. When gel ends up in unplanned spots, puzzles can break. To keep your maps from having gel issues, there are multiple solutions: Take care to not diminish the realism in your map. Anything unpaintable should have an in-game justification.
 * Careful level design -- force the player to abandon gel, reduce portalable and paintable surfaces, use grating on floors, etc.
 * erases gel. Also consider using cleansing gel.
 * makes a texture unpaintable.
 * Displacements cannot be painted. However, displacements are typically reserved for more organically shaped surfaces such as cave walls.

Other notes:
 * Conversion gel is usually the easiest gel to exploit because it opens up more places for portals to reach, creating a cycle of expanding capabilities. It does however need at least the space of a portal to be used.
 * Repulsion gel is also very easy to get out of hand because of its launching power. Even a tiny splat smaller than a portal can be used, and at any angle.
 * Propulsion gel is the hardest gel to abuse. It's only useful on walkable surfaces, and needs a fairly large area to gain significant speed.
 * Paint can reach unexpected areas with angled flings or double flings.
 * Paint bombs will not explode if they hit a surface with an unusually small amount of force. Worst case scenario, players can roll a bomb around and make it explode at any spot on the ground or use it to slightly boost their height.
 * Paint bombs explode prematurely by touching the player.
 * Paint bombs can nudge or be nudged by players and cubes.
 * Paint bombs can reach out further when portal funneling is enabled or disabled, depending on the situation.
 * Paint will slowly lose kinetic energy when continually moving between two portals on a floor. Don't count on gel to always travel a certain speed.
 * Walls painted with repulsion gel combined with a painted floor allows the player to climb to the highest painted spot on a wall. This is because jumping height is always preserved when bouncing on floors, and bouncing on walls will move the player upward slightly.
 * When loading from a save, any midair gel streams being flung from a portal may exhibit strange behavior, such as lost or gained momentum.