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Abstract — The availability of adequate quantities of ultra high modulus polyethylene (UHMPE) fibres has provided the possibility of creating a new range of polymer composites with high energy absorption capabilities. In this paper several aspects of recent research at Leeds University are described. First, there are the possible requirements of the UHMPE fibres in terms of strength, resistance to creep and adhesion to suitable polymeric resins. It has been found that plasma treatment of the fibres with oxygen as the carrier gas produces substantial improvements in adhesion. Although the interlaminar shear strength of composites made with treated fibres is increased it is found that there are only small changes in the mechanical behaviour of the composites. Secondly, comparative data are presented for unidirectional fibre composites where the fibre phase is either wholly UHMPE, Kevlar 49, Carbon EXAS or E—type glass. Results are also presented for hybrid composites which incorporate both UHMPE fibre and one of the commercial fibres. It is shown that these hybrid composites can combine in a useful way the good qualities of UHMPE fibres, especially their very high energy absorption, with other good qualities of the commercial fibres