Simple SummaryDespite recommendations for, and the prevalence of, passive rest amongst heat-exposed occupational groups to mitigate heat stress, there is limited information regarding the effectiveness of this control measure. This systematic review of post-work core temperature cooling rates conferred by passive rest reports that 8 of the 50 included datasets failed to indicate cooling. Of the remaining 42 datasets, only 10 indicated core temperature cooling rates exceeding 0.034 °C min−1or ~0.5 °C per 15 min, with participants wearing athletic attire or similar in each of these studies. Cooling during passive rest while wearing more insulative work attire or similar was only achieved in 7 of 13 datasets. Irrespective of its widespread implementation, these findings indicate that passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Alternative cooling methods are required to mitigate heat stress now and into the future.AbstractPhysical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min−1), and forty-two datasets reported reducing core temperature (−0.002 to −0.070 °C min−1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of −0.004 °C min−1(−0.032 to +0.013 °C min−1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.