Supramolecular fillers were incorporated in a poly(epsilon-caprolactone)-based polyurea in a modular approach via a "perfect-fit" principle. DSC and AFM studies both support the same model in which the bis(ureido) butylene-based filler molecules are incorporated into the bis(ureido) butylene hard segment domains of the polymer via bifurcated hydrogen-bonding interactions up to 23 mol % (= 7.3 wt %) of incorporated filler. Polymer hard segment and filler form a single phase, and the soft phase remains unaffected. This resulted in stiffer materials (23 mol % of incorporated filler more than doubled the Young's modulus) without a decrease in tensile strength or elongation at break. When more than 23 mol % of filler was added to the polyurea, separate filler crystallites were observed in both AFM and DSC. A drop in Young's modulus was now observed, followed by an increase upon adding even more filler. In this second regime, a decrease in tensile strength and elongation at break was observed, revealing similar behavior to reinforcing thermoplastic elastomers with the more common micrometer-sized reinforcement fillers.