We study the structure of the interregional inventor networks in Sweden by examining the residence of inventors and coinventors involved in Swedish patent applications to the European Patent Office. Several factors are found to influence the spatial affinity of regions. We find that spatial affinity extends beyond the region if it has less own R&D-related resources (business R&D, university R&D and patenting); if it is close to the other region and if it is relatively small. The resources of that other region plays a positive role if, in analogue fashion, that region has more R&D-related resources.