This study elucidates the influence of differences in crosslink structure and crosslink density on water tree growth, electrical tree growth, and electrical breakdown strength. One reference LDPE was compared with a LDPE containing a higher number of vinyl groups, introduced via the copolymerisation with a diene. Because of the chemical difference, the initially formed crosslink structure will be different for the materials. A range of various crosslink densities was considered for the two materials. It was found that along with a noticeable change in morphology after crosslinking, significant changes in particularly water tree growth, electrical tree growth, and electrical breakdown strength could be observed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3483-3494, 2011