The invention relates to a roller for generating pressure when joining polymer-based materials, in particular conveyor belts. For this purpose, the roller has two arms (1, 2) that are joined to one another via a joining piece. Respective roller parts (4, 5) are provided at the free ends of the arms, coming into contact with the materials to be joined, and transmitting the pressure into the joining site. The pressure of the roller parts is generated via a pressure device (7) pressing on the arms. For a movement in relation to the materials to be joined, a roller part (5) is driven by a drive (6).