public readonly bool isValid { get; }

The vertex count must be from 3 to PhysicsConstants.MaxPolygonVertices, the radius must be finite and zero or greater, and the centroid, every vertex and every normal must be finite. The vertices must also form a convex hull that keeps every one of them, so a vertex that would be welded away or dropped makes the geometry invalid. See _areEdgesValid for the rules that decide which vertices survive.