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Asahi Kasei clarifies the mechanism of cooling stockings for the first time in the world by fluid-solid conjugate heat transfer analysis

- Result published online in Scientific Reports -

April 13, 2020
Asahi Kasei Corp.

Asahi Kasei has clarified the mechanism of “cooling stockings,” which provide a cooling effect when worn, by quantitative analysis using computational fluid dynamics (CFD) together with surface morphology analysis. This world-leading result was published in Scientific Reports, an online journal issued by Nature Research[1]. Simulations were performed by the Computer Aided Engineering Dept., Production Technology Center, Corporate Production Technology, and their results were verified and validated by the R&D Laboratory for Applied Product, Fibers & Textiles R&D Planning and Business Development, Performance Products SBU.

People often wear stockings to warm their legs. Ordinary textile materials are thermally insulative, which prevents body heat from dissipating. In contrast, it is known that some knitted stockings promote heat release and have a cooling effect. Unlike products that feel cool to the touch, cooling stockings have the effect of physically cooling the body surface when they are worn. This effect had previously been confirmed by heat radiation experiments using a thermal metallic body. However, the mechanism of physically cooling the body had not been clarified.

  • The cooling effect of knitted stockings shown by the change of human leg temperature after walking (a, b). Upper images are before walking, lower images are after, with bare legs (a) and cooling stockings (b). Microscope images (c) of commonplace stockings (upper) and cooling stockings (lower). Note that the cooling stockings are knitted with wider spacing between yarns along the vertical direction.

To clarify the phenomenon, we devised a numerical model of the protrusions (ribs) on the surface of the cooling stockings, and investigated natural convection[2] along the periodically formed minuscule ribs utilizing fluid-solid conjugate heat transfer analysis[3] with CFD. As a result, we concluded that the cooling effect emerged from the micrometer-size ribs. Contrary to common garments, which have a heat retention effect when worn, the micrometer-size ribs produce a cooling effect as the heat radiation from the ribs is promoted by natural convection.

  • Model diagram of rib
    Model diagram of rib

    P: pitch between ribs
    e: diameter of rib (diameter of yarn)

The report entitled “The cooling mechanism of minuscule ribbed surfaces” can be viewed at the

following address

Our clarification utilizing fluid-solid conjugate heat transfer analysis represents a valuable result both industrially and academically. The mechanism thus clarified makes it possible to add cooling functions to textile products depending on the structure of the fibers and fabrics. The development of apparel products which provide comfort while reducing energy usage would be expected to significantly contribute to sustainability.

Asahi Kasei will continue to contribute to life and living for people around the world by providing value-added products and services by combining computer aided engineering (CAE) together with various other technologies in addition to fiber technology.

  • [1]Scientific Reports is an open access online journal publishing original research from across all areas of the natural and clinical sciences. It is issued by Nature Research, which publishes the notable science magazine Nature and more than 90 other journals.
  • [2]Natural convection is a type of flow in which the fluid motion is generated only by temperature gradients, not by any external source.
  • [3]Fluid-solid conjugate heat transfer analysis is a method of continuous coupling analysis of fluid and solid. The solid affects the temperature of the fluid, which makes the fluid move and creates flow velocity, leading to a change in the temperature of the solid.