Introducing 3D modeling - Introduction to AutoCAD 2011: 2D and 3D Design - page 246

Fig. 12.34 Example - constructing the Line outline
The stages of producing the extrusion are shown in Figs 12.34 and 12.35.
The resulting 3D model is a surface model.
N o t e
The resulting 3D model shown in Fig. 12.35 is a surface model because
the extrusion was constructed from an outline consisting of lines,
which are individual objects in their own right. If the outline had been
a polyline, the resulting 3D model would have been a solid model. The
setting of MOde makes no difference.
The Sweep tool
To call the tool click on its tool icon in the Home/Create panel
( Fig. 12.36 ).