# Chain definition reference for the Physics Core 2D API > Explore the properties you can use to configure a physics chain in the Editor. > **Note:** > > This documentation is about writing C# scripts using the `Unity.U2D.Physics` API. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to [2D physics](/engine/6000.6/manual/unity2d/2d-physics.md.md) instead. Explore the properties you can use to configure a chain shape in the Unity Editor using the Physics Core 2D API. ## Surface Material The properties in the **Surface Material** section determine how the shape interacts with other shapes. | Property | Description | | ----------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Friction** | Sets the coefficient of friction for this collider. A value of 0 means no friction, like ice. A value of 1 means very high friction, like rubber. The default is 0.6. | | **Bounciness** | Sets how bouncy the surface is, and how much other colliders bounce off it. A value of 0 means the surface is not at all bouncy, like soft clay. A value of 1 means the surface is very bouncy, like rubber. The default is 0. | | **Friction Mixing** | Determines the method Unity uses to mix the friction of two objects when they make contact. The options are:**Average**: Uses the average of the two values.**Mean**: Uses the geometric mean of the two values. The geometric mean multiplies the two values then returns the square root.**Multiply**: Multiplies the two values together.**Minimum**: Uses the smaller value.**Maximum**: Uses the larger value. | | **Bounciness Mixing** | Determines the method Unity uses to mix the bounciness of two objects when they make contact. The options are:**Average**: Uses the average of the two values.**Mean**: Uses the geometric mean of the two values. The geometric mean multiplies the two values then returns the square root.**Multiply**: Multiplies the two values together.**Minimum**: Uses the smaller value.**Maximum**: Uses the larger value. | | **Friction Priority** | Determines which shape contributes its **Friction Mixing** mode when two shapes come into contact. Unity uses the **Friction Mixing** mode from the shape with the highest **Friction Priority** value. If the two shapes have the same **Friction Priority** value, Unity uses the highest `SurfaceMaterial.MixingMode` enumeration value from the two shapes. | | **Bounciness Priority** | Determines which shape contributes its **Bounciness Mixing** mode when two shapes come into contact. Unity uses the **Bounciness Mixing** mode from the shape with the highest **Bounciness Priority** value. If the two shapes have the same **Bounciness Priority** value, Unity uses the highest `SurfaceMaterial.MixingMode` enumeration value from the two shapes. | | **Rolling Resistance** | Sets how resistant the shape is to rolling. The range of values is 0 to 1, where 0 means no rolling resistance and 1 means full rolling resistance. | | **Tangent Speed** | Sets the speed the surface moves other objects that come into contact with it, in meters per second. For example, if you set **Tangent Speed** to 5, the surface acts like a conveyor belt that moves objects along the surface at 5 meters per second. You can use a positive or negative value to set the direction of movement. | | **Custom Color** | Sets the color Unity uses to draw the debug visualization of the shape. The alpha value is ignored. For more information, refer to [Draw a debug visualization of objects](/engine/6000.6/manual/unity2d/2d-physics-api/create-objects/debug-drawing.md). | ## Contact Filter The properties in the **Contact Filter** section determine which other shapes the shape collides with. For more information, refer to [Configure collisions between objects](/engine/6000.6/manual/unity2d/2d-physics-api/interactions/collisions-enable.md). | Property | Description | | --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | **Categories** | Sets the layers this shape belongs to. | | **Contacts** | Sets the layers this shape collides with. | | **Group Index** | Assigns the shape to a group, and overrides the **Categories** and **Contacts** properties. Use the following values:0: Assigns no group. The shape uses the **Categories** and **Contacts** properties to determine collisions.Positive value: The shape always collides with other shapes that have the same **Group Index**.Negative value: The shape doesn't collide with other shapes that have the same **Group Index**. | ## Other properties | Property | Description | | ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | **Is Loop** | Connects the first and last vertices of the chain to form a loop. | | **Trigger Events** | Produces a trigger event when the shape starts and ends overlapping another shape that has its **Is Trigger** property enabled. To fetch events, refer to [`PhysicsWorld.triggerBeginEvents`](/engine/6000.6/script-reference/unity/u2d/physics/physicsworld/triggerbeginevents.md). | | **World Drawing** | Draws the chain when Unity draws the debug visualization of the world. For more information, refer to [Draw a debug visualization of objects](/engine/6000.6/manual/unity2d/2d-physics-api/create-objects/debug-drawing.md). | ## Additional resources * [Create an object with the Physics Core 2D API](/engine/6000.6/manual/unity2d/2d-physics-api/create-objects/physics-object.md) * [Configure Physics Core 2D API scenes with definitions](/engine/6000.6/manual/unity2d/2d-physics-api/properties/definitions.md) * [Configure global Physics Core 2D API settings](/engine/6000.6/manual/unity2d/2d-physics-api/properties/class-physics-core-settings2d.md)