V-Ray Material Outlines

Enable Outlines – When enabled, adds outlines to the object the material is applied to. This option is disabled by default.

Line Color – Determines the color of the outlines. A Texture can be applied.

Line Width – Determines the width of the outlines in pixels. The soft limit is 100. Click on the  arrow to expand. A Texture can be applied.

Opacity – Determines how opaque the lines are. Click on the  arrow to expand. You can attach a Texture for the opacity. The Mix Strength option determines the percentage of blending between the Opacity value and the texture.

Outer Overlap Threshold – Determines when outlines are created for overlapping parts of the object. Lower values reduce the outer overlapping lines, while higher values produce more overlapping outer lines.

Normal Threshold – Determines at what point lines are created for parts of the object with varying surface normals (for example, at the inside edges of a box). Lower values mean that only sharper normals generate an edge, while a value of 0.5 means that 90 degrees or larger angles generate internal lines. Higher values mean that smoother normals can also generate an edge. Don't set this value to pure 1.0, as this fills curved objects completely. 

Overlap Threshold – Determines when outlines are created for overlapping parts of the object. Lower values reduce the internal overlapping lines, while higher values produce more overlapping lines. Don't set this value to pure 1.0, as this fills the objects completely. 

Inner Line Control – When enabled, allows the inner line to be edited further. This option is disabled by default.

Inner Line Color – Determines the color of the inner lines. A Texture can be attached 

Inner Line Width – Determines the width of the inner lines in pixels. Click on the  arrow to expand for the Texture option, where you can attach a texture to serve as the inner line width.