The vibration damping property of plant fibres composites is of practical interest for commercial applications of biobased and eco-composites. Damping behaviour has been observed by experimentation and exploited in the marketing of sporting equipment but the origins of this behaviour have so far been only based on conjectures. In this thesis, the damping capacity of plant fibre composites was attributed to their chemical composition and the reversible interactions enabled by the breaking and reforming of hydrogen bonds under stress. The approach to explaining the mechanisms started with the characterisation of different plant fibre types to search for correlations between their physical and chemical structure. The investigation continued with quantifying the effect of hydrogen bonding compounds such as water, glycerol and polyglycerol on the damping coefficient of fibres and reinforced composites. The results of the polyol impregnation indicated that applying a pretreatment enhanced the vibration damping performance of flax reinforced composites, validating the hypothesis of the essential role played by hydrogen bonds in the fibres. The improvement in the damping coefficient of the composites was shown to be to the detriment of their stiffness. The compromised between the two properties was investigated in the final part of this thesis by using hybrid flax-carbon fibre reinforced composites.