The power law and the Herschel-Bulkley model are common ways of representing the behaviour of a number of food materials. The underlying relations contain parameters which are obtained by fitting to experimental results. There is evidence to suggest that both models can represent materials equally well and this is investigated. With the Herschel-Bulkley model, it is shown that good fits can be obtained to data points with significantly different values of the parameters, including the particular case of the power law. This arises due to a linear relation between certain logarithmic terms. This is characterised and used to provide a means for converting between good triples of Herschel-Bulkley parameters. The fact that the two models behave equally well raises the question as to whether it is better to use the power law (being the simpler) for predictive work in the design of production systems where the materials experience medium to high shear rates in pipelines. (C) 2007 Elsevier Ltd. All rights reserved.