In the present investigation the influence of strain rate and temperature on modulus, strength and work of fracture of high-performance polyethylene (HPPE) fibre is studied. At low temperature and/or high strain rates the fibre shows brittle failure, displaying a pronounced strain rate and temperature dependence of the tensile strength. At high temperatures and/or low strain rates a transition from a brittle to a ductile failure mode could be observed. This brittle-to-ductile transition is analysed in terms of competitive failure modes, which leads to a simple model that can be used to predict the strain-rate dependence of the transition temperature. In the brittle failure mode it is observed that an increase in strain rate and/or decrease in temperature leads to a reduction in work of fracture. This reduction could successfully be predicted by combining a previously published mathematical model for the deformation of HPPE fibres with the observed strain-rate dependence of the tensile strength. From the numerical simulations it can be deduced that a constant minimum level for the fracture energy will be reached at high strain rates or low temperatures.