Inter-yarn friction helps to increase energy absorption in ballistic fabrics. This paper reports on the results of sol-gel treatment on aramid yarns to increase the inter-yarn friction. Two types of TiO2/ZnO hydrosols (submicro-sized and nano-sized) prepared using hydrolysis and peptization methods were used to treat aramid yarns with and without curing. SEM was used to characterize the change in morphology. FTIR and EDX analyses were applied to identify the coating substance. The inter-yarn friction was tested using Capstan method. Images from SEM showed that the surface of the yarn treated with TiO2/ZnO submicro-sized hydrosol was covered with lump-like coating whilst in the case of TiO2/ZnO nano-sized sol treatment, the coating on the fibres was more film-like. The substance in the coating was confirmed as titanium dioxide and zinc oxide by FTIR and EDX analyses. The test results for coefficient of friction revealed that the coefficient of friction between the yarns treated by submicro-sized hydrosol was 54% higher than the non-treated, and the nano-sized hydrosol was associated to a 10% increase. However, the curing process had little effect on the coefficient of friction between yarns. The study also showed that the tensile properties of the treated yarns and the weight add-on were not significantly affected. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.