This study reports the ballistic penetration performance of a composite material composed of woven Kevlar(R) fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol). The impregnated Kevlar fabric yields a flexible, yet penetration resistant composite material. Fragment simulation projectile (FSP) ballistic penetration measurements at similar to244 m/s have been performed to demonstrate the efficacy of the novel composite material. The results demonstrate a significant enhancement in ballistic penetration resistance due to the addition of shear thickening fluid to the fabric, without any loss in material flexibility. Furthermore, under these ballistic test conditions, the impregnated fabric targets perform equivalently to neat fabric targets of equal areal density, while offering significantly less thickness and more material flexibility. The enhancement in ballistic performance is shown to be associated with the shear thickening response, and possible mechanisms of fabric-fluid interaction during ballistic impact are identified. (C) 2003 Kluwer Academic Publishers.