The response to electron beam irradiation of poly(ethylene-co-1,9-decadiene) was examined and compared to a reference polyethylene. The polymers were produced in a low-pressure process using a chromium-based catalyst giving relatively high levels of inherent unsaturations through thermal termination of the polymerisation. The copolymerisation with 1,9-decadiene gave an additional 63% vinyl end groups. A dramatic improvement in the crosslinking response was observed for the decadiene polymers and consequently considerably smaller radiation doses were needed to obtain a certain degree of crosslinking. The reason for the improved response was the overall higher amount of vinyl groups as well as the placement of vinyl groups along the molecular weight distribution; the longer molecules contained more vinyls than the shorter ones. A certain amount of vinyls remains after irradiation. It is likely that the restricted mobility due to the crystalline structure makes these vinyls less accessible for reaction. Elongation at break data at room temperature exhibited significant differences between the reference and decadiene materials, although M-c determinations showed little difference in actual crosslinking density. This is likely to depend on the changes in the amorphous part of the material where the crosslinks are formed whereas the M-c calculation is based on the same concentration of crosslinks but they are instead spread in the whole material. Therefore, larger differences could be seen in the solid state.