Portals

Portals are the feature gameplay mechanic of the Portal series. Portals are placed by firing the Handheld Portal Device; they work in pairs where they allow two-way movement through each Portal. A player can place blue and orange portals in Singleplayer, or in Co-op: As Atlas, blue and cyan; and as P-body, red and orange. Lone portals appear as a solid-coloured oval and paired portals a colour-bordered oval - with the "center" being a window to the other Portal. Portals are capable of maintaining the mass and velocity of any object that passes through one portal and exits out the other. Portals are also capable of maintaining the flow of light and gravity, specifically the Excursion Funnels and Light Bridges.

World Portals
Within certain levels there are World Portals. These are invisible portals that can be used to create the illusion of a larger area.

Bugs

 * Portal boosting A player is able to boost their momentum when travelling through two portals placed on the floor by using their primary or secondary fire key as they exit the primary or secondary portal, respectively.  This is caused by the Portal mechanic pushing the player away from a portal if the portal is re-placed somewhere else (or in this case, in the same place).