Shear and extensional flow properties of the melts of high-density polyethylene (HDPE)-maple composites were studied with capillary rheometry to understand the effects of the wood content, particle size, and maleated polyethylene (MAPE). The viscosity data were compared with the values for neat matrix resin for reference. The effects of commercial wood particle size grades were examined at 60% by weight of wood loading. It was found that both shear and extensional viscosities increase with wood content but the filler content dependence is not as significant as for suspensions of inorganic fillers at similar filler loadings. Commercial wood particle size grades were found to result in less change in viscosity than wood content. The Mooney analyses conducted on the lower branch of the capillary shear flow data revealed a significant contribution of wall slip and confirmed the presence of a yield stress at higher filler contents. The internal lubrication role of MAPE was also illustrated in detail through the changes in both shear and extensional flow. (c) 2005 Society of Plastics Engineers.