Sweat-sensitive adaptive warm clothing

Abstract

Thermal regulation in warm clothing is essential for enhancing human comfort in cold environments. However, traditional warm clothing lacks the ability to adapt to dynamic changes in the human body's microenvironment. Here, we present an adaptive warm cloth, featuring a filling made of a natural bacterial cellulose membrane that responds to human sweating. The cloth's thickness automatically adjusts from 13 millimeters (under low humidity and no sweating conditions) to 2 millimeters (under high humidity and sweating conditions), expanding the thermal regulation capability by 82.8% compared to traditional warm clothing with an unchanged thickness of 13 millimeters. Modeling results further suggest that deploying this adaptive warm clothing across 20 cities in China could extend the duration of the no thermal stress zone by an average of 7.5 hours. Combining exceptional thermal regulation, high stability, and scalability, this clothing represents a notable supplement to existing thermal management technologies.

Fig. 1.. Concept and mechanism of the SAWC.

(A) Working rationale of the SAWC. (B) Heat flux q of the SAWC as function of thickness h; h is defined in the inset. The regions I to III represent the summer (Sum.; left), spring and autumn (Spr. Aut.; middle), and winter textiles (Win; right), respectively. (C) A comparison of normalized thickness (h_normal) between our membranes and reported hygroscopic materials under different relative humidity (RH). The background color from white to green represents the environmental state from dry to humid. The normalization is based on h of our membrane at a relative humidity of 20%. (D) Optimization of material parameters of the membrane by modeling. E_A, the elastic modulus of the active layer; h_A, the thickness of the active layer; and w_t, the residual thickness of the membrane, as defined in the inset. The dashed line marks the threshold force required to support the textile.

Fig. 2.. Fabrication and characterization of the membrane.

(A) The fabrication process of the membrane. UV, ultraviolet. (B) An image of the large-scale membrane. (C) A 3D plot of the membrane’s stable bending angle (θ_s) versus the relative humidity and the thickness of PET. (D) Evolution of the bending angle (θ) of the membrane (BC10-PET30) with time at different humidity levels. The two parts separated by a vertical dashed line represent the evolution and steady stages of the bending angle, respectively. (E) Cycling stability of the membrane (BC10-PET30). Insets schematically illustrate membranes at a relative humidity of 20% (top) and 95% (bottom), respectively.

Fig. 3.. Optimization and characterization of the SAWC.

(A) The influence of the membrane’s shape on its residual thickness. (B) Thickness of a single unit containing different round membranes (d = 3 or 4 cm) as a function of relative humidity (inset: the dimensions of the single pocket). (C) Effect of the size of round pores in the lining on the response time required for humidity change within the pocket. (D) Time-dependent thickness of a single unit containing a round membrane (d = 4 cm) under relative humidities of 20 and 95%. (E and F) The temporal (E) and cycling stability (F) of the single unit under relative humidities of 20 and 95%. Insets show a single unit under relative humidities of 20% (top) and 95% (bottom). (G) Normalized heat flux (q_normal) of different types of textiles. Traditional textile (TT) #1, commercial polyester shirt (~1.4 mm thick); traditional textile #2, commercial down coat (~13 mm thick). Error bars represent the SD of five independent measurements. (H) Water vapor transmittance (WVT) of the device with/without membrane. (I) Washing stability of the single unit. The thickness of the individual unit at different relative humidities (20 and 95%) after each washing cycle.

Fig. 4.. Design of the SAWC and outdoor application.

(A and B) Optical (left) and infrared images (right) of the SAWC in dry (A) and humid (B) states. There is nothing in the “5” pocket, but there are down feathers in the “6” pocket and membranes in all other pockets. (C and D) Thickness (C) and normalized heat flux (q_normal) (D) of the SAWC when walking and cycling. The normalization process is based on the heat flux of “5” in the walking state.

Fig. 5.. Modeled comfortable time and income growth for urban outdoor workers.

(A) The comparison of comfort time per day between sanitary workers with warm clothing and SAWC on different dates. The comfort time is the sum of the slight cold stress (−1.5 to ~−0.5), no thermal stress (−0.5 to ~0.5), and slight heat stress zone (0.5 to ~1.5). The blue (Warm clothing-no) and orange colors (SAWC-no) with patterns represent the no thermal stress zone of workers with warm clothing and SAWC, respectively. The blue (Warm clothing-slight) and orange colors (SAWC-slight) without patterns represent the sum of slight cold and heat stress zones of workers with warm clothing and SAWC, respectively. (B) The comparison of comfort time of different workers in Nanjing on 1 January 2024. (C) The comparison of comfort time for sanitary workers in different cities on 1 January 2024. (D) The comfort time (left), its difference (mid), and income growth (right) of sanitary workers with warm clothing and SAWCs in 20 cities in China on 1 January 2024. The blue and orange circles in the left map represent the comfort time of sanitary workers with warm clothing and SAWCs, respectively. The circles composed of a blue semicircle and an orange semicircle represent the comfort time that is 24 hours for sanitary workers with warm clothing and SAWCs. The values are scaled to the diameter of the circle.