The structure/property relationships in the PE fibres have been interpreted quantitatively using a microfibrillar model and the low-strain mechanical properties have been analysed using the Takayanagi models. Information obtained from Raman spectroscopy in the previous paper has been analysed to determine the molecular deformation behaviour of the gel-spun polyethylene (PE) fibres. It is demonstrated that there is a bimodal distribution of stress in the crystalline regions : due to the two-phase microstructure of the fibres and it has been shown that the molecular deformation behaviour can be interpreted quantitatively using a parallel-series model. It is found that the Young’s modulus of the crystalline regions increases with the degree of chain extension and for the highest-modulus fibres may be close to the theoretical modulus of polyethylene. The fibre modulus is reduced by the presence of low-modulus non-crystalline material in parallel with the crystals.