Gels

Gel is a gameplay implement introduced in Portal 2. They are paint-like liquids that impart different effects on surfaces and objects.

Propulsion Gel
The bright orange Propulsion Gel greatly increases the player's velocity. Objects covered in Propulsion Gel have their friction reduced, causing them to slide around.

Repulsion Gel
Repulsion Gel is a light blue substance that repels objects. A player or an object that hits a surface coated with it bounces off. Jumping off such a surface launches the player higher than a normal jump. Objects (such as Storage Cubes and Turrets) can be covered in Repulsion Gel, which causes them to bounce around erratically on all types of surfaces.

Conversion Gel
Conversion Gel is a portal-conducting white liquid. It enables the player to place portals on surfaces that normally do not support portals.

Water
Water washes off other gels from surfaces and objects. It has no special properties and does not stick to surfaces.