-from the mesh boundary inwards.</li>
-<li><b>Faces (Edges) without layers</b> - defines geometrical faces
- (or edges in 2D) on which element layers should not be
- constructed. By default the element layers are not constructed on
- geometrical faces shared by solids (and edges shared by faces in 2D).
+ from the mesh boundary inwards.</li>
+<li><b>Extrusion method</b> (available in 3D only) - defines how
+ positions of nodes are found during prism construction and how
+ the creation of distorted and intersecting prisms is prevented.
+<ul><li><b>Surface offset + smooth</b> method extrudes nodes along the normal
+ to the underlying geometrical surface. Smoothing of the internal surface of
+ element layers is possible to avoid creation of invalid prisms.</li>
+ <li><b>Face offset</b> method extrudes nodes along the average normal of
+ surrounding mesh faces to the intersection with a neighbor mesh face
+ translated along its own normal by the thickness of layers. The thickness
+ of layers can be limited to avoid creation of invalid prisms.</li>
+ <li><b>Node offset</b> method extrudes nodes along the average normal of
+ surrounding mesh faces by the thickness of layers. The thickness of
+ layers can be limited to avoid creation of invalid prisms.</li>
+\image html viscous_layers_extrusion_method.png "Prisms created by the tree extrusion methods at the same other parameters"
+</ul></li>
+<li><b>Specified Faces/Edges are</b> - defines how the shapes specified by
+ the next parameter are used.
+<li><b> Faces/Edges with/without layers</b> -
+ defines geometrical faces or edges on which element layers
+ either should be or should not be constructed, depending on the
+ value of the previous parameter (<b>Specified Faces/Edges are</b>).
+ Faces (or edges) can be selected either in the Object Browser or in
+ the VTK Viewer. \b Add button becomes active as soon as a suitable
+ sub-shape is selected.