Superfine down powder was produced from down fiber after it was cut into short pieces and ground on a purpose-built machine. Scanning electron microscopy photographs showed that the down fiber was ground into particles with some fiber fragments and a large amount of rod-shaped ultrafine powder. Particle size distribution analysis indicated that the average size of the down powder was 1.546 mu m. Fourier transform infrared analysis showed that the absorbing peaks around 1640, 1520, and 1230 cm(-1) were sharper than those of the down fiber. X-ray diffraction analysis revealed that the crystallinity of the superfine down powder was a little lower than that of the down fiber. Thermogravimetric analysis showed that the thermal stability decreased when the down fiber was ground into powder. Differential scanning calorimetry analysis showed that the intensity of the heat-absorbing peaks of the down powder was lower than that of the down fiber, so the down powder decomposed more readily than the down fiber. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2204-2209, 2009