Conversion Gel

Conversion Gel is the white paint-like gel in Portal 2 that makes a surface accept portals. It is one of three gels: orange Propulsion Gel speeds the player across a surface and blue Repulsion Gel bounces them off it. The gels came from Tag: The Power of Paint, whose team joined Valve and merged their paints with Valve's fluid-dynamics code; the third Tag paint, which let the player walk on any surface regardless of gravity, gave playtesters motion sickness and was replaced by Conversion Gel because it fits the portal mechanic. Supergiant Games' Windows release of Bastion includes a weapon inspired by the gel and by Portal 2's turrets.