Capsule properties such as shell-wall modulus and burst strength have great influence on capsule suitability as a mechanical trigger in a self-healing composite. The elastic modulus and failure behavior of a poly(urea-formaldehyde) shelled microcapsule was determined through single capsule compression tests. A shell theory model for the compression of a spherical fluid-filled shell was utilized to extract the shell-wall modulus values from the load-displacement data. The model assumed constant encapsulated volume and a linear elastic shell-wall constitutive relationship. Average shell-wall modulus was ca. 3.6 GPa, independent of capsule diameter. However, burst strength was found to be highly dependant on capsule diameter.