Background: Pressure ulcers are a risk for bedridden patients and various supports exist to prevent them. The Pressure Relief Index (PRI) evaluates pressure relief of dynamic mattresses over time. This study compared the PRI of the SUMMIT mattress (AKS-France) and the NIMBUS 3 (HNE Medical).Methods: In this non-blinded, randomized, crossover, non-inferiority study, patients aged ≥60 with a BMI of 16-35 kg/m2, predominantly confined to bed, able to walk with aid and with pelvic symmetry were recruited from a hospital rehabilitation department from March-April 2012. Exclusion criteria included past or present pressure ulcers, inability to remain supine and deep vein thrombosis. Peak pressures of the sacrum were recorded at 0.1 Hz during a single complete 10-min inflating cycle on both mattresses, with the order determined via electronic randomization allocation.Results: Thirty-one subjects were included and randomized; with 14 finally analyzed in the SUMMIT-NIBMUS 3 order group and 16 in the NIMBUS 3-SUMMIT group. The difference in PRI <30 mmHg between the two mattresses was 13.2% [0.3-26.1] (p < 0.05), allowing a non-inferiority - superiority switch. The SUMMIT mattress demonstrated a significantly higher percentage of time <30 mmHg (p = 0.0454). No significant difference in mean minimal pressure was seen (p = 0.3231) and mean maximal pressure was in favor of SUMMIT mattress (p = 0.0096). BMI did not affect pressure profile. There were no adverse events.Conclusions: Evaluated by the PRI, the SUMMIT mattress had a better interface pressure profile than the NIMBUS 3 in older patients. The PRI is a promising tool for clinical decision-making and research, warranting validation.