New experiments of fiber deposition in the human respiratory airway were conducted by delivering aerosolized man-made fibers (TiO(2) and glass) into two different human respiratory airway casts at three inspiratory flow rates. Fiber deposition patterns and regional deposition efficiencies in the airway casts were studied and compared with previously published results acquired from Carbon fiber. The results showed that very few small momentum fibers (TiO(2) and glass fibers) were deposited in the airway casts, which is significantly different from the results found for the large momentum fiber (carbon fiber). The fiber deposition pattern and deposition efficiency in the two airway casts were similar in both trend and magnitude, and all of the data revealed an overall continuity between fiber materials. Empirical models were proposed based on the experimental data acquired for estimating the fiber's regional deposition efficiency in the human respiratory airway. (C) 2008 Elsevier Ltd. All rights reserved.