The invention relates to a polymer composition comprising a polymer (a)and a nanoparticle filler (b), wherein the polymer composition comprises a weight percentage (wt. %) of the nanoparticle filler (b) which is A, wherein A is 0.05 wt. %,or more, and wherein the polymer composition has a first nanoparticle aggregate ratio which is B, wherein B is 0.50, or less, wherein a first aggregate size is defined as a cluster of nanoparticles with a cluster size larger than d1, wherein d is 1.0 μm; an electrical device, e.g. a power cable; and a process for producing an electrical device.