Fiber morphology with off-standing branches, as found in nature, e.g., in goose downy feather, provides exquisite functions that can be barely achieved by man-made fiber systems. In this work, we develop a simple and scalable method for generating downy feather-like para-aramid fibers and assemblies. Through treating commercial para-aramid microfibers with mild alkaline solution (low concentration of NaOH), a synergistic effect of chemical hydrolysis and physical shearing is successfully triggered to generate abundant nanofiber branches on the surface of para-aramid fibers. When compared with conventional monotonous structures, nonwovens composed of downy feather-like fibers exhibit a typical multiscale fiber morphology, larger specific surface area and smaller pore size, thus showing enhanced particles adsorption capacity (over twice of the pristine nonwoven), excellent oil absorption capacity (increased by ~ 50%), improved air filtration performances (doubled the filtration efficiency) and effective thermal insulation (thermal conductivity = 26.1 mW·m⁻¹·K⁻¹). More attractively, the intrinsic flame-retardant nature of para-aramid is well inherited by the downy feather-like fibers, and the fabrication process requires neither sophisticated equipment, nor tedious procedures, making us believe the strong competitiveness of these fibers and assemblies.