Polyurea microcapsules were prepared by sequential interfacial reaction of different aromatic and aliphatic isocyanates. The resulting composite capsule walls were studied using scanning transmission X-ray microscopy (STXM) to quantitatively map the distributions of the resulting aromatic and aliphatic polyureas across the capsule wall. Application of this method to both cross-linked and non-cross-linked polyurea capsules resulted in observation of different capsule wall growth mechanisms, depending mainly on the choice of monomers.