# Calculate accurate reflection and refraction
To create more detailed reflection and refraction in a scene, use a Proxy Volume. A Proxy Volume is a 3D shape onto which HDRP projects a 2D color buffer or cubemap texture that contains a rendered scene.
In the Unity Editor, this component is called a Reflection Proxy Volume, but HDRP uses the component to calculate more accurate effects in both reflection and refraction.
## How reflection and refraction use a Proxy Volume
HDRP projects the color buffer or the cubemap texture from a Reflection Probe or a Planar Probe onto a Proxy Volume. HDRP then uses the Proxy Volume to calculate the depth of the point a reflected or refracted vector hits.
HDRP determines this based on a [reflection and refraction hierarchy](how-hdrp-calculates-color-for-reflection-and-refraction.md).
## Assign a custom Proxy Volume to a Reflection Probe
By default, a Reflection Probe uses the shape and size of its [Influence Volume](Reflection-Probe-Usage.md#use-an-influence-volume) as its Proxy Volume.
To assign a custom Proxy Volume to a Reflection Probe, do the following:
1. In **Projection Settings**, disable **Use Influence Volume As Proxy Volume**.
2. Select **Add Component** and select **Reflection Proxy Volume**.
3. In the **Reflection Proxy Volume**, set the shape and size of the Proxy Volume.
4. In the probe's **Projection Settings**, use **Proxy Volume** to select the Proxy Volume you created.
The **Shape** of the Proxy Volume must match the **Shape** of the Reflection Probe.
- Use **Box** if the **Shape** of the Reflection Probe is **Box**.
- Use **Sphere** if the **Shape** of the Reflection Probe is **Sphere**.
- Use **Infinite** with either Reflection Probe shape.
If you disable **Use Influence Volume As Proxy Volume** in a probe's **Projection Settings** but leave **Proxy Volume** empty, the Proxy Volume has the **Infinite** shape by default.
You can reuse the same Proxy Volume with other Reflection Probes, as long as the shapes match. This is useful if you use multiple Reflection Probes in a single room, because you can reuse one room-shaped Proxy Volume for all the probes.
## Resize a Proxy Volume
Use the Scene view Gizmo to visually modify the size of the **Box** and **Sphere** shapes. Click and drag the handles to move the boundaries of the Proxy Volume.
## Properties
| **Property** | **Description**|
|-|-|
| **Shape** | Define the shape of the Proxy Volume. The possible values are:
• **Box**. Sets the shape as a box. Use **Box Size** to change the size of the box.
• **Sphere**. Sets the shape as a sphere. Use **Radius** to change the size of the sphere.
• **Infinite**. Sets the shape as an infinite volume. You can't adjust the size of this volume. If your Material uses the planar refraction model and the nearest Proxy Volume uses the **Infinite** shape, refraction might not be noticeable.
The **Shape** of a Proxy Volume must match the **Shape** of the Reflection Probe or Planar Reflection Probe that uses it, unless you use **Infinite**. |
## Additional resources
- [Reflection in HDRP](Reflection-in-HDRP.md)
- [Use the appropriate Proxy Volume in refraction](create-a-refractive-material.md#use-proxy-volume).