Headwear includes a crown of planar fabric panels sewn together in-plane, a brim and a size adjuster of a strip of fabric on a lower portion of the crown, around an entirety of a circumference of the crown or a part of the circumference of the crown. The size adjuster includes, in a space defined by a casing formed by the strip of fabric, a shape-changeable component that, at heat of a predetermined temperature or higher, is configured to soften and extend in a circumferential direction of the crown by a length that is greater than a length by which the shape-changeable component extends at heat lower than the predetermined temperature, in response to a tensile force applied to the shape-changeable component in the circumferential direction of the crown. The fabric panels have a contour and a mesh formed by cutting fabric on a bias.