In one example in accordance with the present disclosure, an additive manufacturing system is described. The additive manufacturing system includes a build material distributor to deposit layers of powdered build material onto a bed to form a three-dimensional (3D) printed object. The additive manufacturing system also includes a controller to interrupt printing of the 3D printed object and to resume printing of the 3D printed object. The additive manufacturing system also includes a heat source to, during an interruption in printing, maintain a temperature of a top surface of the powdered build material between a solidification temperature and a melting temperature for the build material.