The Varying Thickness feature is a subfeature to the 
Homogenized Shell feature. It allows to set a spatially or temporally varying thickness. This is typically used for modeling material deposition and such. For more information on varying thickness and the homogenized shell, see the 
Homogenized Shell feature.
 
    Enter a value or expression for the Selected layers thickness dl (SI unit: m). May depend on location, time, temperature, or other quantities. The default value is 0.1 mm.