Erbani R, et al. – This research was planned to determine the impact of relative humidity on preterm infants in closed incubators and calculated their heat loss and additional metabolic cost. Investigations disclosed that relative humidity from days 1-8 was below the recommended target value for preterm infants and resulted in high evaporative and greater total body heat loss and additional metabolic cost. These findings highlighted numerous challenges, including nursing care and incubator design.