button cell batteries or dry batteries are sufficient to drive the fabrics heating to an approximate temperature for human body within 2 s. In addition, the electrothermal fabrics exhibit a fast drying and deicing ability for practical applications in extreme environmental conditions. The electrothermal stability of fabrics under human motions like bending and twisting is also demonstrated. Figure 1a schematically shows the fabrication procedure of GF. Golden graphene oxide (GO) film was prepared by barcoating of GO solutions, and then reduced by hydroiodic acid solution. The reduced graphene oxide (RGO) film was then thermally annealed at 3000 °C and mechanically compacted, giving rise to graphene film with shiny silver gray metallic luster ( Figure 1b). The graphene film was further cut into given size of ribbons with smooth edge by a fine roller blade and twisted into GFs by an electric motor. The diameter of prepared GFs can be controlled from 100 µm to 2 mm by tuning the thickness of thermally annealed graphene films from 5 µm to 30 µm. Optical image of GF wound on a tweezer is shown in Figure 1c, and the GF displays a spiral shape after release ( Figure 1d). The microstructure of GFs is further characterized by scanning electron microscope (SEM). As shown in Figure 1e-g, the GF exhibits regular helical structure with a uniform diameter of 150 µm, which is similar to carbon nanotube fibers prepared by twisting aligned carbon nanotube forests. [40,41] The GFs with unique helical structures display an attractive flexibility, which is a vital requirement for wearable devices. The highly flexible GFs are successfully tied into diverse knots, such as the cross knot (Figure 1h), the carrick bend knot ( Figure 1i) and the flat knot ( Figure 1j). Moreover, GFs are easily stitched into crossstitches with various patterns, such as the embroidery in ZJU style (Figure 1k). No evident fracture is observed during knotting and embroidering, indicating the superb flexibility of GFs.The typical stress-strain curve of GFs is given in Figure 2a. Under uniaxial tensile, the GF first experiences an elastic deformation at a strain below 8%, which is ascribed to the intrinsic elasticity of twisted helices within low deformation range. Upon further stretching, the twisted helices deformed, leading to a large plastic deformation up to 70% before fracture. The record fracture strain of GF is almost seven times higher than the maximum value among reported GFs. [38] Moreover, the GF exhibits a progressive failure from the tensile strain 70% to 220% with fracture toughness of 22.45 MJ m −3 . Figure S1 (Supporting Information) shows the SEM images focused on the fracture surface of a broken GF, revealing a ductile fracture feature. The helix adjacent to the fracture area is slightly unraveled while graphene sheets are dragged out.We believe that the outstanding stretchability of GFs is mainly attributed to their hierarchical structures. The particular Smart wearable clothing [1][2][3] is coming into people's horizon on the basis of rapid...

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