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Puzzle Mechanics

By ScotUpdated

Tactical Quick Answer

Portal 2 adds six major systems on top of the original portal physics: gels, Thermal Discouragement Beams, Hard Light Bridges, Excursion Funnels, Aerial Faith Plates, and new cube types. Every puzzle in the game is one of these elements combined with the portal gun, so learning how each behaves turns the solutions into a matter of finding the right combination. Conversion Gel is the most important addition because it makes any coated surface accept portals.

Portal 2 builds on the original game's physics with six major new systems: gels, lasers, Hard Light Bridges, Excursion Funnels, Aerial Faith Plates, and new cube types. Every puzzle in the game is a combination of these elements with the portal gun. Learn how each one works and the solutions come down to figuring out the combination.

Portal Placement Rules​

The core rules from Portal 1 carry over unchanged:

  • Blue portal on left click, orange portal on right click. One of each active at any time.
  • Portals stick to flat, light-colored surfaces. White Aperture Science panels are the standard.
  • Momentum carries through portals. Speed and direction are preserved relative to the exit portal's orientation.
  • Emancipation Grills erase both portals and destroy carried objects.
  • Portals are two-way. Objects and players pass through in both directions.

What is new in Portal 2:

  • Conversion Gel creates portalable surfaces. Any wall, floor, or ceiling coated with white Conversion Gel accepts portals, even surfaces that normally reject them. This is the primary way to create new portal locations in Old Aperture (Chapters 6 and 7).
  • Some surfaces have changed. Portal 2 uses a slightly different set of panel textures. If your crosshair shows the portal outline, the surface works. If it does not, it will not.

Momentum and Flinging​

Same physics engine, same rules. Fall into a floor portal, launch out of a wall portal at the speed you built during the fall. Deeper drops produce faster launches.

Portal 2 gives you more tools to build speed:

  • Propulsion Gel runways. Coat a floor with orange gel, sprint across it, and hit a portal at the end. You enter much faster than a normal run.
  • Repulsion Gel chains. Bounce off blue gel into a portal for extra vertical speed.
  • Aerial Faith Plate launches into portals. A Faith Plate can throw you into a portal at a fixed speed, which then redirects you based on the exit portal's angle.
tip

When a puzzle combines gel with flinging, coat the surface first, then set up your portals. Trying to place portals while sliding on Propulsion Gel is possible but much harder than doing it from stable ground.

Thermal Discouragement Beams​

Lasers. A red beam fires from an emitter and travels in a straight line until it hits a surface, an object, or a catcher (receptor). When a beam connects to its catcher, it powers a mechanism: a door, a platform, a bridge emitter, or another device.

Rules:

  • Lasers travel in straight lines and cannot bend on their own.
  • Lasers pass through portals. Fire one end of a portal pair into the beam's path, and the beam exits the other portal in a new direction.
  • Lasers pass through glass. They are stopped by cubes and other props.
  • Lasers pass straight through Hard Light Bridges. A bridge will not break a beam, so do not plan a solution around blocking one that way.
  • Touching a beam pushes you away with a sizzle and does a small amount of damage. It is not the instant kill it looks like, and dying to one takes deliberate, repeated exposure.
  • Multiple catchers can exist in a single room. Each one needs its own beam.

Discouragement Redirection Cubes​

The primary tool for redirecting lasers. These cubes have a built-in lens that catches a laser beam and re-emits it from the opposite face.

How to use them:

  1. Pick up the cube and carry it into the beam's path.
  2. The cube catches the beam automatically.
  3. Rotate the cube by changing your facing angle while holding it. The beam follows.
  4. Aim the redirected beam at the catcher.
  5. Set the cube down. It holds position and keeps the beam connected.

You can chain multiple redirection cubes to route a beam around corners, through portals, and across rooms. Some puzzles require three or four cubes in sequence.

warning

Dropping a Redirection Cube while it is actively redirecting a beam can send the beam in an unexpected direction. Set the cube down gently on a flat surface. Throwing it scatters the beam.

Hard Light Bridges​

Flat, solid surfaces made of light. They extend from wall-mounted emitters and travel in a straight line until they hit a solid surface. You can walk on them, crouch behind them, and use them to block hazards.

Rules:

  • Hard Light Bridges pass through portals. Place a portal in the bridge's path, and the bridge extends out of the other portal in the new direction.
  • Bridges block turret fire. Stand behind one and turrets cannot hit you.
  • Bridges block laser beams. A bridge between a laser and its catcher cuts the connection.
  • Bridges serve as floors over toxic goo and pits. Place a portal on a wall above a gap, redirect the bridge through it, and walk across.
  • Bridges do not move objects. They are static surfaces. Objects placed on them stay put.

Common uses:

  • Creating walkways over goo or bottomless pits.
  • Shielding yourself from turret fire.
  • Building platforms at specific heights by redirecting the bridge through portals at different elevations.
  • Blocking and unblocking laser paths to activate mechanisms in sequence.

Excursion Funnels​

Tractor beams. Wide, cylindrical tubes of blue light that carry players and objects in one direction. They emit from wall-mounted devices and travel until hitting a solid surface.

Rules:

  • Standing in a funnel moves you in the direction it flows. You float, and you can aim and fire portals freely. You keep some lateral control and can steer yourself out whenever you like. What you cannot do is move against the flow.
  • Objects placed in funnels float and travel with the flow. Cubes, turrets, and even gel drops move through funnels.
  • Funnels pass through portals. Place a portal in the funnel's path, and it extends from the other portal.
  • Polarity reversal. Some chambers have buttons that reverse the funnel's flow direction. Press the button and everything in the funnel starts moving the opposite way.
  • Funnels do not damage you. They are safe to enter and exit.

Common uses:

  • Floating across gaps that are too wide to fling.
  • Transporting cubes to locations you cannot carry them to on foot.
  • Reversing direction mid-flight to reach platforms above or below the funnel's default path.
  • Combining with portals to create vertical elevators or redirect horizontal funnels to vertical ones.
info

Funnels move you slowly. If a puzzle feels like it is taking too long, you are probably not meant to ride the funnel the entire distance. Look for a portal shortcut that lets you enter the funnel closer to your target.

Aerial Faith Plates​

Spring-loaded catapults embedded in the floor. Step on one and it launches you along a fixed parabolic arc. You cannot control the trajectory once airborne.

Rules:

  • Faith Plates launch players and objects. Step on one, get launched. Drop a cube on one, it gets launched too.
  • The arc is essentially fixed, because the plate sets your velocity outright instead of adding to whatever you arrived with. Launch speed does vary slightly with where on the plate you land, and your air control is only suppressed for a short window the mapper sets, so you will miss the intended target if anything other than gravity acts on you afterwards.
  • You can place portals at the landing zone. The Faith Plate throws you, and you enter a portal at the top of the arc or at the landing point, redirecting your momentum.
  • All Faith Plates are floor-mounted. There are no wall or ceiling versions. One floor plate late in Chapter 9 launches you sideways, which is the only real exception to the usual up, forward or backward arcs.

Common uses:

  • Crossing large gaps without fling setups.
  • Launching cubes to elevated positions.
  • Chaining Faith Plate launches with portal redirections to reach areas neither tool can reach alone.

Mobility Gels​

Gels are paint-like liquids that coat surfaces and change their physical properties. They pour from ceiling-mounted pipes and dispensers. Once a gel hits a surface it stays there until water washes it off.

Repulsion Gel (Blue)​

Bounces anything that contacts the coated surface. The bounce height is proportional to the incoming speed. Fall from higher, bounce higher.

Rules:

  • Coating a floor with blue gel turns it into a trampoline. Walk onto it and you bounce lightly. Fall onto it from height and you launch upward.
  • Coating a wall with blue gel bounces you away from the wall on contact.
  • Cubes and turrets bounce off blue gel surfaces.
  • Crouching while standing on blue gel suppresses the bounce. Useful for positioning without launching yourself.

Propulsion Gel (Orange)​

Accelerates anything moving across the coated surface. Walking on orange gel turns a stroll into a sprint. Running on it builds speed fast enough to cross large gaps with a jump at the end.

Rules:

  • Coating a floor with orange gel creates a speed runway. You accelerate rapidly while moving across it.
  • Coating a ramp or angled surface with orange gel launches you off the edge at high speed.
  • Cubes slide across orange gel instead of stopping.
  • Combining orange gel with portals is the fastest way to build speed for distance flings in the Old Aperture chapters.

Conversion Gel (White)​

Makes any surface portalable. The most strategically important gel in the game.

Rules:

  • Most walls, floors, and ceilings coated with white gel accept portal placement, including metal panels, concrete, and dirt. There are three real exceptions: gel cannot be applied to transparent surfaces such as glass, it passes straight through grating, and a surface that is not flat or not large enough to fit a portal stays unportalable no matter how much gel is on it. That last one rules out pipes and other curved geometry.
  • Cubes and turrets cannot be coated with Conversion Gel at all.
  • White gel is your primary tool in Old Aperture (Chapters 6 and 7), where almost no surfaces are portalable by default.
  • White gel dispensers are always positioned to let you coat specific surfaces. If you cannot reach a dispenser, redirect its output through portals or funnels.

Water (sometimes called Cleansing Gel)​

Washes gel off surfaces and objects. Pours from certain pipes and dispensers. It is not really a gel: internally it is an eraser and not a paint, and it has no properties of its own beyond removing what other gels have applied.

Rules:

  • Water removes any gel it touches. Blue, orange, or white gel washes away on contact with water flow.
  • Useful for resetting surfaces. If you coated the wrong area, find a water source to clean it.
  • Some puzzles require you to wash gel off a surface to change how that surface behaves.

Gel Interaction Rules​

  • Gels travel through portals. Redirect gel output through a portal to coat a distant surface.
  • Gels travel through Excursion Funnels. A funnel can carry gel drops to surfaces the dispenser cannot reach directly.
  • Only one gel can coat a surface at a time. Applying a new gel replaces the old one.
  • Emancipation Grills do not remove gel. Water does. The two are different systems entirely: the Grill erases portals and vaporizes objects, while water is what cleans a coated surface or a coated cube.
tip

When you enter a room with gel dispensers, look at the dispenser positions first. Where the gel can reach tells you where the puzzle wants you to go. Place portals to redirect gel before trying to redirect yourself.

Cubes​

Portal 2 has four cube types, up from the original game's two.

Cube TypeWhat It Does
Weighted Storage CubeStandard cube. Holds down buttons, passes through portals. Same as Portal 1.
Weighted Companion CubeStorage cube with hearts. Mechanically identical. Returns in a brief but memorable scene.
Edgeless Safety CubeA sphere. Rolls freely. It can hold down the standard Super Button, and the restriction that catches people out is per-receptacle instead: a sphere receptacle takes only a sphere. Used almost entirely in co-op, with one single-player appearance as garbage.
Discouragement Redirection CubeHas a built-in lens. Catches and redirects Thermal Discouragement Beams. See the laser section above.

Frankenturrets​

A turret fused with a Storage Cube. It walks around on stumpy cube legs and makes distressed turret sounds. Frankenturrets function as weighted objects: pick them up and place them on buttons. They are Wheatley's creations and appear across Chapters 8 and 9, not in Chapter 5. Chapter 5's turret factory is where the Defective Turrets live, which are a different thing.

Sentry Turrets​

Same behavior as Portal 1 with minor visual updates:

StateBehavior
StandbyMotionless with weapons retracted. This is the resting state.
SearchingThe red targeting laser sweeps. This happens after losing a target, and it returns to standby after about three seconds.
AlertOpens its chassis, speaks a line, and takes a moment to deploy its weapons before firing.
DisabledTipped over. Fires frantically in all directions, then deactivates permanently.

Turrets tip over from physical contact: portal tricks, cube drops, or pushing them from behind. Hard Light Bridges block their fire, and in fact stop them detecting you at all. Portal 2 adds two more ways to disable one that the first game did not have: a Thermal Discouragement Beam, and Repulsion Gel. Excursion Funnels will carry a turret around but do not disable it.

Portal 2 introduces Defective Turrets in Chapter 5. They are out of ammunition, so firing produces only a clicking sound, and some were assembled sideways. Left alone they tend to catch fire and explode. Their voice is the opposite of a monotone: Nolan North plays them as humorous and sarcastic, in a masculine and noticeably less robotic register than the standard turret.

info

Turrets in Portal 2 are less common than in Portal 1. Sentry turrets debut in Chapter 3 (Turret Intro, Turret Blocker, Laser Vs Turret) and return in Chapter 5's factory. Chapter 8 is Wheatley's track, where the turret-shaped things you meet are Frankenturrets and not sentries. When turrets do show up, the room always has a tool to deal with them.

Emancipation Grills​

Same as Portal 1. Translucent blue barriers that:

  1. Erase both active portals.
  2. Destroy physics objects carried through them (cubes, turrets).
  3. Remove gel from surfaces and objects near the barrier.

Portal 2 uses grills more aggressively. Some puzzles require you to complete actions on one side of a grill, then intentionally walk through it to reset your portals before setting up a new configuration on the other side.

Toxic Goo​

Brown-green liquid. Contact deals continuous damage that kills you within a few seconds and never instantly. Objects that fall in are usually just deleted once they drop out of sight, though Portal 2 sometimes shows them fizzling on the way down, which the first game never did.

In Portal 2, goo appears frequently in the Old Aperture chapters and in Wheatley's test chambers. Hard Light Bridges are the primary tool for crossing goo-filled areas.

Advanced Movement​

These techniques are not needed for the main campaign but are useful for speed and challenge completions:

  • Gel speed boosting. Sprint across Propulsion Gel, jump at the end of the runway, and enter a portal. The gel speed carries through the portal for maximum launch distance.
  • Funnel hopping. Enter an Excursion Funnel, fire portals while floating, and drop out of the funnel at the exact right moment. Useful for reaching platforms adjacent to the funnel path.
  • Faith Plate portal combos. Let a Faith Plate launch you, then place a portal in your landing zone mid-flight. You enter the portal with the Faith Plate's momentum and exit wherever the other portal is aimed.
  • Crouch-jumping. Jump and then press crouch to pull your feet up. It gives extra clearance on ledge landings. It does not extend how far you travel horizontally, since ducking changes your collision hull and not your velocity.

Developer Console​

Portal 2 runs on the Source Engine, which includes a developer console for debugging, experimentation, and modding. The console is not enabled by default.

Enabling the console:

  1. Open Options > Keyboard/Mouse.
  2. Set Allow Developer Console to Enabled.
  3. Press the tilde key (~) during gameplay to open the console.

Most of the commands below require sv_cheats 1 first, though sv_portal_placement_never_fail and portal_draw_ghosting do not:

CommandWhat It Does
noclipDisables collision. Fly through walls and geometry freely.
godInfinite health. Turrets, lasers, and goo cannot kill you.
notargetTurrets ignore you completely.
sv_portal_placement_never_fail 1Forces portals to stick to any surface, bypassing the white-panel requirement.
ent_create_portal_companion_cubeSpawns a Companion Cube at your crosshair.
ent_create_portal_weighted_cubeSpawns a Weighted Storage Cube at your crosshair.
portal_draw_ghosting 0Disables the X-ray outline of portals through walls. Used by the mapping community for cleaner visuals.
warning

Enabling sv_cheats blocks achievements and Challenge Mode record submissions. The console message says "this app session", but the engine actually tracks it per level, so loading or reloading a map with sv_cheats 0 restores tracking. You do not need to restart the game. In multiplayer the setting is controlled by the host.

Cut Content​

Two gel types were developed for Portal 2 but removed before release. Their code partially remains in the engine's files.

Adhesion Gel (Purple)​

Designed to let players walk on walls and ceilings, inherited from the student project Tag: The Power of Paint, whose team Valve hired. It was cut for two reasons: playtesters found the inverted perspective nauseating and disorienting when trying to work out portal trajectories, and the gel did not work correctly with portals.

It was not removed cleanly. Adhesion survives as paint type 1 in Valve's own entity definitions, labeled "Stick" and described there as scrapped wall-walking paint with no effect in the released game. Its emitter is still in the files, and one leftover behavior still functions: cubes coated in Propulsion Gel will not slide across an Adhesion Gel floor.

Reflection Gel​

Reflection Gel reflects lasers. Painted onto a wall, floor, or ceiling, it bounces a Thermal Discouragement Beam off the surface the way a Discouragement Redirection Cube does. Valve's own notes record that paint type 1 was "retconned into laser-reflection gel in dlc1", meaning the Peer Review update reused the abandoned Adhesion slot for it.

It uses a slightly darker texture than Conversion Gel. It was never exposed to players in any official content.

note

The anti-Propulsion behavior you may have read about, where coated objects stop sliding, is real but it is Adhesion Gel's leftover property, not what Reflection Gel is for. The two get conflated because they share an internal slot.

Speedrunning Techniques​

The Portal 2 speedrunning community is highly active. Single-player has no Any% category: it splits into No SLA, where the record stands around 55 minutes, and SLA, where it is around 36 minutes. Co-op does have an Any%, at roughly 18 minutes. These techniques are used by competitive runners but are not needed for casual play.

  • Save/Load Abuse (SLA). The community's actual name for save-glitching, and a leaderboard category in its own right. It covers using any unnatural load or level transition to make something possible that otherwise is not, such as save-load clipping. It is about clipping through geometry and not skipping cutscenes.
  • Player Physics Deformation (PPD). Rotating one of your physics shadow collision boxes so that it partially separates from your normal collision, which allows clipping through walls and boosting yourself and props. It is triggered by dropping a physics prop inside your shadow hitbox, or teleporting the shadow into a static prop.
  • Crouch Flying Glitch (CFG), also called Funnel Fly. It preserves the anti-gravity of an Excursion Funnel after you have left it. Note that you have no control over your vertical movement while doing it, which makes softlocks easy, so treat it as an advanced technique and not a beginner one.
  • Reportal. Shoot the portal you are entering, immediately after you pass through it, for roughly 200 units per second of extra speed. It is a timing trick on an existing portal, not a two-portal fling setup. Since the Peer Review patch, doing this on floor surfaces no longer gives a boost.
note

"Portal bumping" is not an exploit and not a technique name. Bumping is the engine's own portal placement step, where it nudges a portal to fit around edges and other portals. The func_portal_bumper entity that mappers place is a usability aid that helps portals land, not a barrier against cheating.

Frequently Asked Questions​

What does each gel do in Portal 2?

Repulsion Gel (blue) bounces anything that touches the coated surface, and the bounce height scales with your incoming speed. Propulsion Gel (orange) accelerates anything moving across it. Conversion Gel (white) makes any wall, floor, or ceiling accept portals.

How do you redirect a laser in Portal 2?

Carry a Discouragement Redirection Cube into the beam path, then rotate it by changing your facing angle while you hold it until the re-emitted beam points at the catcher. Set the cube down gently so it holds position. Lasers also travel through portals, so a portal pair can bend a beam without a cube.

How do I turn on the developer console in Portal 2?

Open Options, go to Keyboard/Mouse, and set Allow Developer Console to Enabled, then press the tilde key during gameplay. Cheat commands like noclip and god require sv_cheats 1 first, and enabling cheats disables Steam achievements for that session.

Can Hard Light Bridges block turrets and lasers?

Yes. Bridges stop turret fire, so you are safe standing behind one, and a bridge placed between a laser and its catcher breaks the connection. They also pass through portals and work as walkways over toxic goo and pits.

Was there a purple gel cut from Portal 2?

Adhesion Gel was designed to let you walk on walls and ceilings but was cut during playtesting because players felt severe nausea and disorientation calculating portal trajectories while inverted. A second cut gel, Reflection Gel, entered the file architecture during the Peer Review DLC update and was never exposed to players in official content.