A roll forming apparatus includes at least one forming roll being spaced from a forming body to define a gap. The forming roll includes a working zone portion having a working zone surface with a length extending along a rotation axis of the forming roll and a thermal resistance boundary extending at an acute angle relative to the rotation axis. In further examples, methods include the step of feeding a stream of molten glass through the gap to form a glass ribbon including a formed thickness. The thermal resistance boundary facilitates substantial uniform radial expansion of the working zone surface relative to the rotation axis across the length of the working zone surface in response to heating of the working zone portion by the molten glass.