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Liquid fiberglass insulator
Pongthep Charnchaichujit (original design)
- Used as far back as 1971 by Aperture Science, this orange and supposedly sweet and largely non-toxic liquid of fiberglass insulation was originally to serve as a diet aid, serving as a dietetic pudding substitute and marketed under the name "Propulsion Pudding". Its purpose was to increase the velocity of any food following it through the digestive tract, leaving the body no time to absorb calories. However it was pulled from shelves when it was discovered that digestion plays several crucial roles in the eating process, such as breaking food into manageable chunks before being violently expelled from the human body. The Propulsion Pudding was subsequently renamed "Propulsion Gel", and made for use with the ASHPD in Test Chambers instead, while another attempt at a dietetic pudding substitute, the Repulsion Gel, was tested.
- As a testing element, Propulsion Gel accelerates the velocity of any object it touches, giving them largely increased speed capabilities and allowing them to vault over pits or reach the far end of a long expanse quickly enough to best a ticking clock. Propulsion Gel is spilled through a vent, and plays quite well with portals. Placing one portal under a vent and another in different area of a Test Chamber allows the use of the Gel far from the vent, allowing progress past a given obstacle.
- While normal run speed is 175 inches/sec, running along the Propulsion Gel can boost the speed of a Test Subject up to 800 inches/sec.
- Run speed on a flat ground covered in Propulsion Gel accelerates at a rate of 500 inches/sec² and 100 inches/sec² on ramps. This means that on flat ground it takes over a second to reach full speed, while on a ramp it takes half that.
- If a Weighted Storage Cube is coated with Propulsion Gel, it will automatically slide on any incline. While this is not used in the single-player campaign, it is an element in the final course of the co-op campaign.
- "Propulsion Gel" is a registered trademark of Aperture Science.
 Related Achievements
|Stranger Than Friction (15G)|
|Master the Propulsion Gel. Play on the phrase "Stranger than fiction".|
 Behind the scenes
- The Propulsion and Repulsion 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.
- Propulsion Gel mirrors directly the red 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.
- It's revealed in Portal 2 that the three gels were simply not connected to the more modern Aperture facility, explaining why they weren't encountered in the original Portal.
- The Propulsion and Repulsion Gels use the same colors as that of the ASHPD's portals (orange and blue, respectively).
- While the animated diagrams of the Propulsion and Repulsion Gels show them to be contained in buckets, this aspect was not seen in-game.
Being covered with Propulsion Gel in Test Shaft 09.
Propulsion Gel icon in Perpetual Testing Initiative.
 List of appearances
- Portal 2 (First appearance)
- Peer Review
- Perpetual Testing Initiative
- Lego Dimensions (Non-canonical appearance)