> For the complete documentation index, see [llms.txt](https://monasheng.gitbook.io/zerotohero/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://monasheng.gitbook.io/zerotohero/3d-printing-zero-to-hero/advanced-skills/advanced-slicing/shell-thickness.md).

# Shell Thickness

{% embed url="<https://www.youtube.com/watch?v=Ws503QCY6Ts>" %}

{% hint style="info" %}
:man\_mage: **Important:** changing the shell thickness of your printed parts can be a surprisingly effective way to radically increase their strength and stiffness, with comparatively little additional print time/material usage.
{% endhint %}

By default, most 3D printers only provide 1-2 layers of plastic on the outside of a part, with the remainder of the volume made-up of [Infill](/zerotohero/3d-printing-zero-to-hero/advanced-skills/advanced-slicing/infill.md). This is more than sufficient for most nonstructural parts, though increasing the shell thickness can be useful when:

1. you want to alter the strength/stiffness of the part - especially with respect to bending or twisting loads, or,
2. you want to interact with the part mechanically (e.g. tapping a thread in a hole), and require more 'meat' in that area.

## Shell Thickness vs Infill

Both shell thickness and infill can contribute to making a stronger, stiffer part.

In general, however, due to second moment of area, shell thickness provides substantially higher stiffness and bending/twisting resistance than infill, for the same amount of added material, as it is by definition on the outside of a part.

## Changing Shell Thickness

Altering the shell thickness in *PrusaSlicer* is relatively straightforward, though it is not a standard setting that can be changed through the quick-access menu.&#x20;

From the `Print Settings`  tab, under the `Layers and perimeters` menu, you can change:

* the number of *vertical shells* - i.e. how many nozzle-thicknesses you want on the outer, $$z-$$oriented (i.e. side) surfaces of a part, and,
* the number of *horizontal* shells - i.e. the number of layers you want on the outer, $$x-y-$$oriented (i.e. top/bottom) surfaces of a part.

<figure><img src="/files/TWGdjMhv9MSlKfq6YBZv" alt=""><figcaption></figcaption></figure>

*PrusaSlicer* defaults to vertical shell thicknesses in the order of $$0.8;\text{mm}$$ ($$\approx2$$ layers) and horizontal shell thicknesses in the order of $$0.6-1.0;\text{mm}$$.

You might choose to increase shell thickness arbitrarily, to achieve some particular twisting/bending strength in your part, increase wear resistance of sliding surfaces, or to increase it until particular features (e.g. gaps, weak spots, throats, etc.) are fully-solid.

{% hint style="info" %}
:man\_mage: **Important:** Changing shell thickness can be an effective way to strategically change the failure bottleneck of your part without dumping heaps of material into infill.&#x20;
{% endhint %}