In an example, a method includes acquiring, at a processor, a first data model and a second data model. The first data model comprises a representation of at least one property of at least part of a first object and the second data model comprises a representation of at least one property of at least part of a second object. The first and second objects are to be generated in a common additive manufacturing operation. The method may include generating a first print layer model and a second, different, print layer model using the processor by combining at least parts of the first data model and the second data model and generating additive manufacturing instructions based on the first print layer model and the second print layer model.