You placed a floor and somehow you still walk through it. A decoration keeps snagging you. The box you set down won't move no matter what you do.
Almost every collision problem comes down to a combination of three components: Collider, Is Trigger, and Rigidbody.
This article lines up three identical Cubes and changes one setting at a time to turn them into a wall, a pass-through decoration, and a falling box.
What You'll Learn
- What Collider, Is Trigger, and Rigidbody each do
- That the visible shape and the collision shape are different things
- Why "walk into it to push it" isn't reliable in VRChat
- Which layers you're allowed to touch
Start from a scene with a floor. If you don't have one, build it in your first world.
Three components answer three questions
The way to remember it is simple. Each of the three components answers a different question.
| Component | The question it answers | Think of it as |
|---|---|---|
| Collider | Does it have a shape? | The acrylic case over a museum exhibit |
| Is Trigger | Is that shape a wall or a sensor? | An automatic door's infrared beam. Your body isn't stopped, but passing through is detected |
| Rigidbody | Fixed in place, or moved by physics? | Unbolting a shelf from the floor and turning it into cargo |
Without a Collider, anything passes through regardless of shape. With a Collider and Is Trigger off, it stops you like a wall. Turn Is Trigger on and it becomes a sensor you can walk through while still detecting the crossing.
Rigidbody is a separate axis. Add it and the object comes under the physics engine's control — falling under gravity, rolling when hit. Leave it off and the object stays fixed in place.
Floors and walls only need the Collider. The floors and walls you've placed so far don't want a Rigidbody.
The visible shape and the collision shape are separate
One more thing to settle first.
Mesh Renderer draws the visuals; Collider defines the collision shape. They're separate things, and their shapes don't have to match.
A houseplant with finely spread leaves doesn't need per-leaf collision. One box around the pot is plenty in practice. Building collision that matches the visible shape exactly just costs you performance.
The baseline approach is this:
- Wrap roughly with boxes and cylinders (Box Collider, Capsule Collider)
- For shapes like stairs and pillars, combine several boxes
- Use Mesh Collider only for shapes boxes can't express, like terrain
Hands-On: Turn three identical Cubes into three things
Line up three identical Cubes on the floor and change one setting on each. When you're done, the left one stops you, the middle one lets you through, and the right one falls.
Change one thing at a time. Change two at once and you won't know which took effect.
1. Place three Cubes
Create three with "3D Object → Cube" and set names and positions.
| Name | Position (X, Y, Z) | Scale |
|---|---|---|
WallCube | (-1.5, 0.5, 2) | (1, 1, 1) |
PassCube | (0, 0.5, 2) | (1, 1, 1) |
FallCube | (1.5, 2, 2) | (1, 1, 1) |
Only FallCube gets Y 2, floating above the floor so we can drop it later.
Right now all three are identical: a Box Collider, Is Trigger off, no Rigidbody.
Press Play and walk. All three stop you like walls, and FallCube hangs in the air.
2. Make the middle one pass-through
Select PassCube and change Layer at the top right of the Inspector to Walkthrough.
Play and walk, and only the middle Cube lets you through. It looks exactly the same.
Walkthrough is one of VRChat's built-in layers, meaning it doesn't collide with players. Use it for curtains, foliage, thin fencing, hanging signs — anything you want visible but passable.
Removing the Collider instead would let objects placed on it fall through. Walkthrough keeps only players passing through while objects still collide.
3. Make the right one fall
Select FallCube and add a Rigidbody via "Add Component".
Press Play and the floating Cube drops to the floor.
Two Rigidbody settings matter here.
| Field | Meaning |
|---|---|
| Use Gravity | Whether gravity applies. Off leaves it floating |
| Is Kinematic | On stops physics moving it. Position is then driven by scripts |
Turn Use Gravity off for "a floating decoration I don't want to drop," and Is Kinematic on for "something that must never move from this spot."
4. Try it as a sensor
Finally, turn on Is Trigger on WallCube's Box Collider.
Play and you pass right through what used to be a wall. Turning Is Trigger on removes physical collision.
That looks the same as Walkthrough if all you notice is passing through, but there's a difference. Is Trigger reports "someone entered / exited" to your scripts. That's the foundation for showing a sign when someone enters an area, or sending them back when they fall below the floor.
Using that detection is covered in detecting areas with triggers. Here, "Is Trigger on means you pass through" is enough.
Once you've confirmed it, turn Is Trigger back off.
Pushing by walking doesn't suit VRChat
Looking at a box with a Rigidbody, you'd think you could push it around. Know this first.
In VRChat, pushing objects by walking is not reliable.
Players aren't ordinary physics objects — they're treated as a capsule. Body-slam a Rigidbody box and sometimes it pushes, sometimes it stops you like a wall, sometimes a light box goes flying. It can even behave differently in real VRChat than it did in Unity.
So a puzzle about pushing boxes around can't be built this way.
When you want players to move things, make them grabbable.
| What you want | What to use |
|---|---|
| Falls under gravity, rolls when hit | Collider + Rigidbody |
| Players carry it around | VRC Pickup (making objects you can pick up) |
| Follows a fixed motion | Change the position from Udon |
One more thing: Rigidbody objects aren't shared with others by default. A box that rolled on your screen is somewhere else on your neighbor's. Sharing position requires VRC Object Sync.
Pick layers, don't change them
VRChat uses several layers for fixed purposes. The main collision-related ones are these.
| Layer | Meaning |
|---|---|
Default | Ordinary objects. Floors, walls, and furniture go here |
Walkthrough | Players pass through. For decorations |
Pickup | Grabbable objects. Doesn't collide with players |
Player / PlayerLocal | The players themselves. Not something you set |
MirrorReflection | For mirror rendering. Don't use it for walls |
The important part is not changing names or collision settings. Modify them and upload, and VRChat reverts them. Picking from what's provided is fine.
When you want your own layer, use one of the higher-numbered User Layers. Changes there are preserved.
Floors and walls can stay Default. For now, the only layer work you'll do is "set it to Walkthrough when I want players to pass through."
Bonus: Good to Know Up Front
- Mesh Collider has limits: It matches the visible shape, but adding a Rigidbody requires Convex, which can't express complex concave shapes. Outside static terrain, combinations of boxes are the reliable choice
- Overlapping Colliders vibrate: When two collision volumes slightly intersect, they push each other apart and jitter. It happens easily on stairs. Blocking out a room and stairs covers the fix
- Fast-moving objects can pass through: A small object falling quickly can pass through a thin floor. Thicken the floor or raise the Rigidbody's collision detection setting
- Don't add too many physics objects: The more Rigidbodies, the heavier the calculation. Keep rolling objects to a handful and leave decorations fixed
- Players collide with each other too: But via a humanoid capsule, not the visible avatar. A large avatar doesn't get a wider collision volume
Summary
Collision comes down to answering three questions.
- Does it have a shape (Collider), is it a wall or a sensor (Is Trigger), is it fixed or physical (Rigidbody)
- The visible shape and the collision shape can differ. Wrap roughly with boxes
- To let players pass, use
Walkthrough. Removing the Collider drops objects too - Pushing by walking isn't reliable. Make things you want moved into Pickups
The question to ask when a setting confuses you is: "Do I want to let it through, stop it, or drop it?" Settle on one and you know which field to touch.
Next, use this collision to assemble a room. Head to building a room and stairs from Cubes, or start with detecting areas with triggers if you want area detection.