A method of selectively combining particulate material, for example plastics material by sintering, comprises providing a layer of particulate material, providing radiation, for example using a radiation source over the layer, and varying the absorption of the provided radiation across a selected surface portion of the layer to combine a portion of the material of the layer. The method may comprise varying radiation absorption by varying the intensity of the radiation incident on the surface portion of the layer, or alternatively may comprise varying the radiation absorptive properties of the particulate material over the selected surface portion of the layer, for example by printing a radiation absorbent material onto the surface portion.