capping extrusions?

    ExtrudedVisual3D extru = new ExtrudedVisual3D();
                System.Windows.Media.PointCollection collpo = new PointCollection();
                foreach (Point popo in sketchy.points2dlist  )
                {
                    collpo.Add(popo); 
                }
                extru.Section = collpo;
                extru.SectionXAxis = xaxis;
                extru.Transform = groupo;
                extru.Material = new DiffuseMaterial(new SolidColorBrush(colo));
                extru.IsSectionClosed = true;
                 
                Point3DCollection collpa=new Point3DCollection();
               foreach (Point3D po3 in pupo.points3dlist)
                {
                    collpa.Add(po3);  
                }
                extru.Path = collpa;

  
                extru.Fill = new SolidColorBrush(colo);