---
title: "hollow"
subtitle: "Function in std::solid"
excerpt: "Make the inside of a 3D object hollow."
layout: manual
---

Make the inside of a 3D object hollow.

```kcl
hollow(
  @solid: Solid,
  thickness: number(Length),
): Solid
```

Remove volume from a 3-dimensional shape such that a wall of the
provided thickness remains around the exterior of the shape.

### Arguments

| Name | Type | Description | Required |
|----------|------|-------------|----------|
| `solid` | [`Solid`](/docs/kcl-std/types/std-types-Solid) | Which solid to hollow out | Yes |
| `thickness` | [`number(Length)`](/docs/kcl-std/types/std-types-number) | The thickness of the remaining shell | Yes |

### Returns

[`Solid`](/docs/kcl-std/types/std-types-Solid) - A solid is a collection of extruded surfaces.


### Examples

```kcl
// Hollow a basic sketch.
firstSketch = startSketchOn(XY)
    |> startProfile(at = [-12, 12])
    |> line(end = [24, 0])
    |> line(end = [0, -24])
    |> line(end = [-24, 0])
    |> close()
    |> extrude(length = 6)
    |> hollow (thickness = 0.25)
```

![Rendered example of hollow 0](data:image/png;base64,[encoded data, 84228 characters])

```kcl
// Hollow a basic sketch.
firstSketch = startSketchOn(-XZ)
    |> startProfile(at = [-12, 12])
    |> line(end = [24, 0])
    |> line(end = [0, -24])
    |> line(end = [-24, 0])
    |> close()
    |> extrude(length = 6)
    |> hollow (thickness = 0.5)
```

![Rendered example of hollow 1](data:image/png;base64,[encoded data, 136044 characters])

```kcl
// Hollow a sketch on face object.
size = 100
case = startSketchOn(-XZ)
    |> startProfile(at = [-size, -size])
    |> line(end = [2 * size, 0])
    |> line(end = [0, 2 * size])
    |> tangentialArc(endAbsolute = [-size, size])
    |> close()
    |> extrude(length = 65)

thing1 = startSketchOn(case, face = END)
    |> circle( center = [-size / 2, -size / 2], radius = 25 )
    |> extrude(length = 50)

thing2 = startSketchOn(case, face = END)
    |> circle( center = [size / 2, -size / 2], radius = 25 )
    |> extrude(length = 50)

hollow(case, thickness = 0.5)
```

![Rendered example of hollow 2](data:image/png;base64,[encoded data, 98428 characters])


