Use the thickness property to give objects a 3D appearance.
The 3D thickness of an object is the distance that the object is extended above or below its location in 3D. Positive thickness extends upward in the positive Z direction; negative thickness extends downward (negative Z).
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:
A single object cannot simultaneously have different thicknesses.
Changing the 3D thickness property does not affect the appearance of other types of objects.
You can set the default thickness property for new objects you create by setting the THICKNESS system variable. For existing objects, change the thickness property on the Properties palette.
You might need to change the 3D viewpoint to see the effect of thickness on an object.