- Set a Toon BSDF as your model’s material.
- Activate the Freestyle option in the Render Settings, and set Line Thickness,
* More line style settings are found in the Render Layers settings.
* Freestyle lines are only rendered in the final render (F12) and are not rendered in the Cycles viewport interactive render mode.
A more controllable setup:
2 Toon BSDF’s, one for color shading and one for highlights added together, and a Background shader override to control shaded area darkness: