Every face has a single outer loop.

Namespace: Rhino.Geometry
Assembly: RhinoCommon (in RhinoCommon.dll) Version: Rhino 6.0

C#

public BrepLoop OuterLoop { get; }

VB

Public ReadOnly Property OuterLoop As BrepLoop
	Get

Type: BrepLoop

Supported in: 6.0.16224.21491, 5D58w

BrepFace Class
Rhino.Geometry Namespace