public bool IsClosed { get; }

Public ReadOnly Property IsClosed As Boolean
	Get

public:
property bool IsClosed {
	bool get ();
}

Every time this property is accessed, it is computed from scratch, so accessing it multiple times will come at a performance cost. A mesh is closed when each of its edges has two (or more) faces. If an edge has more than two faces (meaning that it's a non-manifold edge), the mesh still may be closed.