One reason human beings wear stockings is to warm their legs. Ordinary textile materials are thermally insulative, which prevents body’s heat from dissipating. In contrary to this common sense, it was discovered that some knitted stockings made up of them permanently promote heat release and cool body. This non-intuitive phenomenon emerges when micro-size yarns are knitted to form wide spacing between neighboring yarns. However, the reason why they cool body was unclear because conventional principles of cooling garments cannot account for it. Here, in the basis of fluid-solid conjugate heat transfer analysis of natural convection, we have clarified the cooling mechanism originates from relative relationship between their geometric structure, a periodic alignment of minuscule ribs, and thermal boundary layer. Our novel finding revealed that sufficiently small ribs on the surface are exposed to steep temperature gradient within thermal boundary layer. Thereby, thermal conduction via ribs is enhanced complementarily as they are separated to guide cooler flow onto the surface. Our study provides a general insight into understanding permanent cooling mechanism on micro-size ribbed surfaces in contrast to conventional theory for heat sink, which is applicable not only to other clothes, but also to artificial devices or natural structures.

人类穿长筒袜的原因之一是要保暖腿部。普通纺织材料具有隔热性，可防止人体热量散发。与这种常识相反，发现一些由它们组成的针织长袜永久性地促进了热量的释放和凉爽的身体。当编织超细纱以在相邻纱之间形成较宽的间距时，就会出现这种非直觉的现象。但是，它们冷却身体的原因尚不清楚，因为冷却衣服的常规原理无法解决。在此，在自然对流的流固共轭传热分析的基础上，我们已经阐明了冷却机理源于它们的几何结构，微小肋的周期性排列和热边界层之间的相对关系。我们的新发现表明，表面足够小的肋在热边界层内暴露于陡峭的温度梯度。因此，当肋被分开以将冷却剂流引导到表面上时，通过肋的导热被互补地增强。与常规的散热器理论相反，我们的研究为了解微型肋状表面上的永久冷却机理提供了一般性见识，后者不仅适用于其他衣服，而且适用于人造设备或自然结构。