FIR-emitting garments produced consistently lower tympanic membrane temperature, reduced mid-sleep sweating, and higher REM sleep proportion compared to control garments, indicating they 'facilitate mild nocturnal heat dissipation and support REM expression' as a passive intervention.
FIR-emitting garments produced consistently lower tympanic membrane temperature (TMT) across the night compared to control garments.
FIR-emitting garments reduced mid-sleep sweating rate compared to control garments.
The proportion of REM sleep was higher in the FIR garment condition compared to the control condition.
A transient increase in low-frequency (LF) heart rate variability power was observed during early sleep in the FIR condition.
The study used a randomized, double-blind, placebo-controlled crossover design with multi-modal wearable sensing to evaluate FIR garment effects on sleep physiology.
This research suggests that pajamas or sleepwear made with far-infrared (FIR)-emitting fabric — a type of textile designed to absorb and re-emit body heat as a specific wavelength of infrared radiation — can subtly change how the body manages heat during sleep. In a carefully controlled study where 15 healthy young men wore either FIR-emitting garments or identical-looking regular polyester garments on two separate nights, those wearing FIR garments had slightly lower core body temperatures (measured at the eardrum) throughout the night and sweated less in the middle of the night. These changes suggest the garments helped the body dissipate heat more efficiently without causing discomfort or overheating. The study also found that people wearing FIR garments spent more time in REM sleep — the stage associated with dreaming and memory consolidation — compared to when they wore regular garments (about 22% vs. 19% of total sleep time). Notably, this improvement in REM sleep happened without any change in total sleep time or overall sleep efficiency. A brief, early-night change in heart rate variability suggested the body was making subtle adjustments to regulate temperature through mechanisms related to blood pressure control, rather than through stress-related pathways. This research suggests that FIR-emitting sleepwear could represent a passive, non-pharmaceutical way to improve the thermal environment during sleep, potentially supporting better sleep quality — particularly REM sleep — in healthy individuals. The findings are based on a small sample of young healthy men in a laboratory setting, so whether these effects extend to other populations, home environments, or individuals with sleep difficulties remains to be studied.
Nishida M, Nishii T, Suyama S, Youn S. (2026). Physiological Effects of Far-Infrared-Emitting Garments on Sleep, Thermoregulation, and Autonomic Function Assessed Using Wearable Sensors.. Sensors (Basel, Switzerland). https://doi.org/10.3390/s26020550