An apparatus comprising: a recoater; an energy source; a carriage supporting the energy source; and a controller to: control the recoater to spread build material particles into a layer on top of a previously applied layer containing fused build material particles; control the carriage to move ahead of the recoater to cause the energy source to apply energy onto build material particles in the previously applied layer prior to the recoater spreading the build material particles onto the previously applied layer, wherein the energy source is to heat the fused build material particles to or maintain the fused build material particles at a temperature above a certain temperature, and wherein the recoater is to be controlled to spread the build material particles on top of the previously applied layer prior to the fused build material particles falling below the certain temperature; and to control the recoater to spread the build material particles while the fused build material particles are in a melted state or gummy state or maintained above a melting temperature of the fused build material particles. a recoater; an energy source; a carriage supporting the energy source; and a controller to: control the recoater to spread build material particles into a layer on top of a previously applied layer containing fused build material particles; control the carriage to move ahead of the recoater to cause the energy source to apply energy onto build material particles in the previously applied layer prior to the recoater spreading the build material particles onto the previously applied layer, wherein the energy source is to heat the fused build material particles to or maintain the fused build material particles at a temperature above a certain temperature, and wherein the recoater is to be controlled to spread the build material particles on top of the previously applied layer prior to the fused build material particles falling below the certain temperature; and to control the recoater to spread the build material particles while the fused build material particles are in a melted state or gummy state or maintained above a melting temperature of the fused build material particles. control the recoater to spread build material particles into a layer on top of a previously applied layer containing fused build material particles; control the carriage to move ahead of the recoater to cause the energy source to apply energy onto build material particles in the previously applied layer prior to the recoater spreading the build material particles onto the previously applied layer, wherein the energy source is to heat the fused build material particles to or maintain the fused build material particles at a temperature above a certain temperature, and wherein the recoater is to be controlled to spread the build material particles on top of the previously applied layer prior to the fused build material particles falling below the certain temperature; and to control the recoater to spread the build material particles while the fused build material particles are in a melted state or gummy state or maintained above a melting temperature of the fused build material particles.