A roll forming apparatus comprising: a glass feed device for supplying a stream of molten glass; and at least one forming roll being spaced from a forming body to define a glass forming gap between the forming roll and the forming body for receiving the stream of molten glass to form a glass ribbon including a formed thickness, wherein the forming roll comprises a working zone portion comprising a working zone surface for engaging the stream of molten glass, the working zone surface including a length extending along a rotation axis of the forming roll, wherein the forming roll includes a first thermal resistance boundary and a second thermal resistance boundary; characterized in that the first thermal resistance boundary and the second thermal resistance boundary comprise frustoconical end surfaces of the working zone portion, frustoconical grooves defined in the forming roll at respective end portions (403, 405) of the forming roll or a first plurality of bores and a second plurality of bores spaced radially around the rotation axis of the forming roll along respective frustoconical surfaces; and the first thermal resistance boundary extends at an acute angle, α, relative to the rotation axis of the forming roll and the second thermal resistance boundary extends at an acute angle, β, relative to the rotation axis of the forming roll, wherein the acute angle of the first thermal resistance boundary and the acute angle of the second thermal resistance boundary are opposite to one another such that the forming roll comprises a circumferential dovetail portion with a trapezoidal cross-sectional portion. a glass feed device for supplying a stream of molten glass; and at least one forming roll being spaced from a forming body to define a glass forming gap between the forming roll and the forming body for receiving the stream of molten glass to form a glass ribbon including a formed thickness, wherein the forming roll comprises a working zone portion comprising a working zone surface for engaging the stream of molten glass, the working zone surface including a length extending along a rotation axis of the forming roll, wherein the forming roll includes a first thermal resistance boundary and a second thermal resistance boundary; characterized in that the first thermal resistance boundary and the second thermal resistance boundary comprise frustoconical end surfaces of the working zone portion, frustoconical grooves defined in the forming roll at respective end portions (403, 405) of the forming roll or a first plurality of bores and a second plurality of bores spaced radially around the rotation axis of the forming roll along respective frustoconical surfaces; and the first thermal resistance boundary extends at an acute angle, α, relative to the rotation axis of the forming roll and the second thermal resistance boundary extends at an acute angle, β, relative to the rotation axis of the forming roll, wherein the acute angle of the first thermal resistance boundary and the acute angle of the second thermal resistance boundary are opposite to one another such that the forming roll comprises a circumferential dovetail portion with a trapezoidal cross-sectional portion.