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- "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]
Used as far back as 1953 by Aperture Science, the Repulsion Gel is the company's first attempt at a dietetic pudding substitute. The gel, a bright blue color, is said to be a sweeter, slightly less non-toxic form of fiberglass insulation. Its purpose was to cause subsequently ingested food items to bounce off the lining of the dieter's distended stomach and out of their mouth. However, for various reasons, the product was also pulled from the shelves like the Propulsion Gel, and reconverted into a testing element for use with the Aperture Science Portable Quantum Tunneling Device, the forerunner of the Aperture Science Handheld Portal Device. The material was eventually deemed hazardous even by Aperture Science's standards, and sealed away in Test Shaft 9 along with the Propulsion Gel and Conversion Gel, before the shaft was opened by Chell in order to escape from it. During the escape, she activated the pump stations containing the gel, and finally opened the main hatch between Test Shaft 9 and the main facility, allowing the Gels to once more become available in the facility.
During a pre-recorded message in a test chamber, Cave Johnson instructed the test subject that they should, under no circumstances, get covered in repulsion gel. Aperture Scientists were not able to identify what element repulsion gel was except that it was "a lively one and it does not like the human skeleton". Despite this, getting covered in repulsion gel in the game will not harm a human or robot player character.
As a testing element, the Repulsion Gel, coming as single blobs or continuous streams through a vent, transfers its properties to any object it touches, giving them a trampoline-like surface. After coating parallel walls on either side of a large pit, a Test Subject ricochets back and forth across the gap. Plastering Repulsion Gel all over a Weighted Storage Cube causes it to barrel across the room, shattering glass and taking out Sentry Turrets in its path. Portals can also be shot under Repulsion Gel vents, allowing the gel to be sent in any area of a Test Chamber.
- "Repulsion Gel" is a registered trademark of Aperture Science.
Behind the scenes
- The Repulsion and Propulsion Gels were first introduced as unnamed paint types in the April, 2010 issue of Game Informer. Gameplay footage and their proper name was revealed during E3 2010.
- So far the expanded gameplay produced by Repulsion Gel and Propulsion Gel alone appears to be extremely satisfying, and Valve indicated a willingness to include more if it sees fit.
- The Repulsion Gel mirrors directly the green paint featured in the student video game Tag: The Power of Paint, as the whole team was hired by Valve to develop it for Portal 2. The original Tag paint was developed by Pongthep Charnchaichujit. The paint variants from both games each work slightly different, though, with the repulsion gel based more reversing vertical momentum (as would a trampoline) while the green paint focused more on jumping itself by having a limited vertical velocity boost.
- There was a Repulsion Gel chamber prior to release that many people think did not make it into the retail game, which it did, in fact, do. It is one of the last chambers of the Repulsion Gel-only levels. Many people do not recognize it because it has been changed in look to match the old facility, and an Aperture Science Material Emancipation Grill was added in front of the ramp.
- While Repulsion Gel was made around 20 years before Propulsion Gel, it hit shelves after Propulsion Gel. Also, there is a face placard about Repulsion Gel saying that is was Aperture's first attempt to create a dietetic pudding substitute, while demonstrational videos say that it was second attempt.
- While the animated diagrams of the Propulsion and Repulsion Gels show them to be contained in buckets, this aspect was not seen in-game.
- The Repulsion and Propulsion Gels use the same colors as that of the ASHPD's portals (blue and orange, respectively).