Create Freeform Surface Offsets
3-D FFS > From surface > Offset 
This function enables you to create offsets of freeform surfaces.
- Identify the required surface by selecting two edges.
- Select further surfaces or end the surface selection with END (RMB).
- Enter the wall thickness.
- Specify whether you want to create an internal or external offset.
Original surface and offset
Shaded offset
Surface from Surface (3-D FFS) • Overview of Functions (3-D FFS)