The development of a novel method for the processing of nascent UHMWPE leading to high ductility and strength extrudates is described. The addition of a surface wetting agent, in this case 10 wt% mineral oil, followed by compaction and extrusion below the melting point leads to the formation of a self-blend of melted and recrystallized UHMWPE and unmelted UHMWPE powders. The presence of the self-blend, indicated by the d.s.c. results, enhances the cohesion between powder particles which leads to an extrudate with more uniform mechanical properties, as demonstrated in Part 2 of this two-part paper. This partial melting during compaction and extrusion is aided by the mineral oil, which also helps to enhance the ductility of the extrudates. The d.s.c. results also provide evidence for chain alignment. The mineral oil acts as a processing aid by allowing the blend to be processed at temperatures at least 10 degrees C higher than are usual for the pure nascent powder. It also acts as a heat transfer agent and solvent for the UHMWPE.