Water treeing - filled versus unfilled cable insulation

Attempts to make XLPE increasingly resistant to water tree growth have involved additives, which decrease hydrophobicity and make the XLPE more like EPR. EPS are evolving through improved processing, clay compatibilization, etc. to reduce losses while retaining the inherent water tree resistance. Thus in the end, the two technologies appear to be moving toward the "center" from opposite ends of a spectrum (filled versus unfilled) to achieve improved cable insulation performance.