Introduction to collider shapes

Colliders are available in different shape configurations. There are three main shape types for collidersAn invisible shape that is used to handle physical collisions for an object. A collider doesn’t need to be exactly the same shape as the object’s mesh - a rough approximation is often more efficient and indistinguishable in gameplay. More info
See in Glossary:

• Primitive colliders are built-in simple shapes, which you can attach to your GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
  See in Glossary and scale to approximately the same size and shape. They are the most computationally efficient shape option, but the least accurate for complex GameObject shapes.
• Mesh collidersA free-form collider component which accepts a mesh reference to define its collision surface shape. More info
  See in Glossary exactly match the shape of the GameObject’s MeshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
  See in Glossary. They are more accurate than primitive colliders, but require more computational resources.
• Wheel collidersA special collider for grounded vehicles. It has built-in collision detection, wheel physics, and a slip-based tire friction model. It can be used for objects other than wheels, but it is specifically designed for vehicles with wheels. More info
  See in Glossary are for in-game items that have physics-simulated wheels (for example, ground vehicles). They have built-in wheel physics, and controls for simulating friction and suspension.

You can also combine several collider shapes to create compound colliders.

In addition, Unity’s TerrainThe landscape in your scene. A Terrain GameObject adds a large flat plane to your scene and you can use the Terrain’s Inspector window to create a detailed landscape. More info
See in Glossary tool has a specific heightmap-based collider, called the Terrain ColliderA terrain-shaped collider component that handles collisions for collision surface with the same shape as the Terrain object it is attached to. More info
See in Glossary.

Additional resources

• Unity Blog: Spotlight Team Best Practices: Collision Performance Optimization (July 2017)