Creo Interactive Surface Design (Style) > Surfaces > Defining Surfaces
  
Defining Surfaces
Use the following chains to define surfaces:
Surface Type
Primary Selection
Closed Loop Requirement for Primary Selection
Secondary Selection
Reparam Curves Supported
Triangular Boundary
3 boundary chains
Yes
0 or more internal curves
Yes
4-Boundary
4 boundary chains
Yes
0 or more internal curves
Yes
Loft
2 or more non-intersecting chains
No
None
Yes
Sweep
1 or 2 guide curves
No
1 or more cross curves
No
Trimmed Rectangle
2 or more boundary curves
Yes
0 or more internal curves
No
 
* The chains you select might define more than one surface. You can trim or extend chains to eliminate ambiguity.