Pressure redistributing (PR) support surfaces are positioned by manufacturers against different levels of patient vulnerability to developing pressure ulcers. However, there is no agreed method through which such linkage between a patient and an appropriate support surface can be made. This lack of clarity leads to new devices being positioned in a manner not representative of their eventual use in clinical practice. Using a data hierarchy approach, three strands of evidence (interface pressure, a pilot national survey and a randomized controlled trial) are presented to illustrate, and support, the repositioning of the Viaclin dynamic mattress overlay (formerly the Pegasus Overture) from use with medium-risk patients to use with higher-risk patients. The need for amendment is seen most strikingly in the two clinical studies featured in this article, during which 87% of all patients nursed on the Viaclin dynamic mattress overlay were at high- to very high-risk of developing ulcers.