The understanding the drug release mechanism from polymeric nanoparticles (PNPs) requires a detailed characterisation of the PNPs internal structure. Small-angle neutron scattering in combination with contrast variation is a unique probe that can provide not only quantitative analysis of core size and shell thicknesses, but also yield the chemical composition of the drug-loaded core. Here we propose a series of experiments to fully characterise the core of our PNPs. This work will also give an insight into any changes to the PNPs polyethylene glycol “stealth layer” which can be tailored to affect the PNPs biodistribution and circulation lifetime, thereby controlling the amount of drug delivered to the patient.