Derek Hull has made many contributions to the elucidation and physical modelling of aspects of the mechanics of materials, conducting pioneering work in applying concepts of materials science to the solution of urgent problems in engineering design. His early work on creep fracture of metals is seminal; he first identified and modelled the underlying mechanism (the diffusional growth of grain boundary cavities, universally known as the Hull–Rimmer mechanism). With Alan Cottrell, he studied the mechanism by which intrusions form and cracks initiate, in fatigue; the Hull–Cottrell mechanism explained the phenomenon in physical terms for the first time. His studies of twinning and fracture in body-centred cubic metals established the mechanism of crack initiation in these metals. He pioneered the study of fracture mechanisms in polymers and in polymer-based composites; his studies of the mechanism of craze formation on polystyrene, and of environmental effects in the fracture of glass-fibre polyester composites are particularly distinguished. He applied his understanding of the failure modes in composites materials to develop successful energy-absorbing structures for the automobile industry.