A clinical investigation was conducted concerning the effects of a newly designed double-layer air-cell overlay in preventing the onset of pressure ulcers for patients with a Braden scale score of < or = 16, and who require a head-elevated position of 45 degrees or higher. A randomised controlled trial was undertaken involving 82 patients from a general hospital ward using one of the following three support surfaces: a double-layer air-cell overlay, a single-layer air-cell overlay or a standard hospital mattress. A significantly lower percentage of patients using the double-layer air-cell overlay developed pressure ulcers (3.4%) compared to 19.2% and 37.0% for those patients using the single-layer air-cell overlay and standard mattress respectively. Based on these findings, a double-layer air-cell overlay should be more effective in preventing the onset of pressure ulcers than either a single-layer air-cell overlay or a standard hospital mattress for subjects requiring head elevation.