Half-Life Wiki
Half-Life Wiki
This subject is from the Portal 2 era.
Coop logo
This article is within the scope of the Portal Project, a collaborative effort to improve articles related to Portal and Portal 2. See the project page for more details about the article status.
Wiki images This article would greatly benefit from the addition of more images.
To illustrate the article add one or more relevant images or upload them from canonical / official sources. For more instructions visit Half-Life Wiki:Images.
Imagecat This article is about the gels. For the Portal 2 co-op chapter, see Mobility Gels (Chapter).

"You're not part of the control group, by the way. You get the gel. Last poor son of a gun got blue paint. Hahaha. All joking aside, that did happen - broke every bone in his legs. Tragic. But informative. Or so I'm told."
―Cave Johnson[src]

The Mobility Gels are special gels used by Aperture Science for testing. Appearing in both single-player and co-op modes of Portal 2, they come in four types: the Repulsion Gel, the Propulsion Gel, Conversion Gel, and the Cleansing Gel.

Propulsion and Repulsion Gels are a derivative of fiberglass insulation designed to be sweeter and slightly less non-toxic. Cave Johnson makes mention of an additional, unknown element in Repulsion Gel which imparts its special abilities, however, Cave warns test subjects that this element "does not like the human skeleton." The gels were originally marketed as a dietary aid, but were quickly pulled from shelves following the disastrous results of their use on humans. The gels were then repurposed as a testing element in Aperture's Test Spheres. Each one has a different effect.

Repulsion Gel[]

The first kind of gel encountered is the blue Repulsion Gel. It is first found when Chell is making her way through Shaft 09's first testing track, where (apparently) war heroes, astronauts, and Olympians were hired to participate in various experiments; one of which was the Repulsion Gel. As the name implies, it causes people and objects to bounce off of it. Testing objects, such as cubes and spheres, will bounce in all directions indefinitely if covered in this gel, until destroyed or cleaned off.

Propulsion Gel[]

The second kind of gel encountered is the orange Propulsion Gel. It is first found when Chell and GLaDOS (still inside a potato after Wheatley's betrayal) make their way through Shaft 09's second testing track, where (presumably) homeless people were offered $60 to for participation in various tests; one of which was the Propulsion Gel. As the name implies, it causes people and objects to move at high speeds while walking/running on it.

If objects are covered in this gel, they will become slippery and slide down any sloped surfaces, which is a useful element in completing some test chambers.

Conversion Gel[]

The third kind of gel encountered is the white Conversion Gel. It was developed on impulse by Johnson; he purchased $70 million worth of Moon rocks and turned them into a gel with similar properties to the company's previous two gels. In doing so, he was fatally poisoned by moon dust. The gel, however, proved to be an excellent portal conductor. Cave decided that testing with this gel will somehow give the scientists a cure for Cave's illness.

It is first found when Chell and GLaDOS are making their way through Shaft 09's third testing track, where Aperture scientists were testing the gel. Being a "good portal conductor" as Johnson put it, it converts any surface into a portal surface. Objects that come into contact with this gel will act as if it's been "cleaned". In other words, if a physics object was covered in Repulsion or Propulsion Gel, the Conversion Gel will remove it - something the Cleansing Gel would do.

Cleansing Gel[]

The fourth and final kind of gel is the clear Cleansing Gel, which is presumably water. With having painted Cleansing Gel onto a surface, will automatically wash off any type of Gel on that said surface. This gel is the least mentioned of them all. At the end of the game during the battle against Wheatley, sprinklers are turned on, cleaning all the gels off the floor, further hinting that this gel is merely water.

This gel can add difficulty to some test chambers, as they will wash off other types of gel the player needs to complete the test, forcing the player to circumvent this. The Cleansing Gel is also useful for removing other gels off of surfaces that would be more helpful not having gels on them. This gel is not seen having its own dedicated pipe pumping it around the facility, unlike the other three.


All four gels share similar properties. They will stick to any solid surface, imparting their properties to that surface. If one type of gel is poured on top of another, it coats the earlier one, negating the properties of the first in favor of its own. The gels immediately wash off in water or Cleansing Gel.

Each gel (apparently) has a harmful effect to it. Cave Johnson warns that the unknown element in the Repulsion Gel "does not like the human skeleton," and the Conversion Gel fatally poisons Johnson, as he said that "ground-up moon rocks are pure poison." However, the harmful poisons in the gels seem to have lost all potency over the course of several decades, as Chell can get splattered with the gels with no effect on her system.

All four gels were left in storage when the old Aperture Laboratories was sealed off. However, the new facility was equipped with pipes to connect to the gel supplies if the old labs were unsealed. This occurs when Chell makes her way out of the facility following Wheatley's betrayal.

Behind the scenes[]

  • The Repulsion Gel and Propulsion Gel are based on the paint featured in Tag: The Power of Paint. The third paint, allowing its user to walk on walls and ceilings, was playtested but ultimately scrapped, although its coding is still present within the game and can be enabled with the correct mods.
  • There are unused gels:
    • Adhesion Gel can be "painted" onto surfaces like any other gel. Originally, the gel was supposed to allow the player to walk on the walls and ceiling of test chambers. However, this effect has been removed in the final game because of playtesters getting motion sickness after using said Adhesion Gel. Objects can be coated in Adhesion Gel, but there are no Adhesion Gel-coated textures for anything, so it will not render. The only remaining effect of Adhesion Gel is that objects coated in it will not slide along Propulsion Gel, and vice-versa. The gel was made purple as a placeholder; a final color was never decided on, so it remains purple in the final game.
    • Reflection Gel, when painted on a wall, floor or ceiling, can reflect lasers off of it, like the Discouragement Redirection Cube, and can be used on the same surface multiple times. The Reflection Gel uses a slightly darker texture than the Conversion Gel, but it does not have the same properties, like making a non-portal conductive surface able to conduct portals.

List of appearances[]