In the present work, the crystallinity and crystalline morphology, thermal stability, water barrier, and mechanical properties of ethylene vinyl alcohol copolymer (EVOH) nanocomposites prepared by melt compounding and incorporating both plant (CNW) and bacterial cellulose nanowhiskers (BCNW) are reported. An improvement in the water barrier performance was observed, that is, 67% permeability drop, only for the microcomposite sample incorporating 2 wt % of bacterial cellulose fibrils. No significant differences in the water-barrier properties of the nanocomposites generated through the two studied preincorporation methods were observed despite the fact that an excellent dispersion was observed in the previous study. On the other hand, direct melt-mixing of the freeze-dried nanofiller with EVOH resulted in increased water permeation. The aggregation of the filler in the latter nanocomposite was also ascribed to the detrimental effect on the mechanical properties. Interestingly, by using the precipitation method, an increase in the elastic modulus and tensile strength of approximate to 36 and 22%, respectively, was observed for a 3 wt % BCNW loading, which was thought to coincide with the percolation threshold. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013