Abstract: Images of fusible toner particles on flexible sheet material, such as applied to paper sheets in electrostatic photocopying machines, are fixed to the material by feeding it through a heating zone in which the particles are softened without fusing them and then passing the material through the nip between smooth rigid pressure roller surfaces which are constantly pressed together under a force sufficiently great to join the heated toner particles superficially one to another and to the sheet structure without forming them into brittle resinous films. An apparatus for carrying out the fixing comprises a set of smooth rigid feed rollers constantly pressed together, preferably by structures like those used for the pressure rollers, under a selected pressure suited for advancing the material into and through a radiant heating zone at a constant speed and thence into the nip of the pressure rollers which are driven at the same peripheral speed.