Use the thickness property to give objects a 3D appearance.
The 3D thickness of an object is the distance that object is extended, or thickened, above or below its location in space. Positive thickness extrudes upward in the positive Z direction; negative thickness extrudes downward (negative Z). Zero (0) thickness means that there is no 3D thickening of the object.
The orientation of the UCS when the object was created determines the Z direction. Objects with a non-zero thickness can be shaded and can hide other objects behind them.
The thickness property changes the appearance of the following types of objects:
Modifying the thickness property of other types of objects does not affect their appearance.
You can set the default thickness property for new objects you create by setting the system variable. For existing objects, change the thickness property on the Properties palette.
The 3D thickness is applied uniformly to an object; a single object cannot have different thicknesses.
You might need to change the 3D viewpoint to see the effect of thickness on an object.