Microcapsules containing a solvent and reactive epoxy resin are a critical component for the development of cost-effective, low toxicity, and low flammability self-healing materials. We report a robust in situ encapsulation method for protection of a variety of oil soluble solvents and reactive epoxy resins surrounded by a thin, polymeric, urea-formaldehyde (UF) shell. Resin-solvent capsules are produced in high yield with diameters ranging from 10 to 300 mu m by controlling agitation rates. These capsules have a continuous inner shell wall and a rough exterior wall that promotes bonding to a polymer matrix. Capsules as small as 300 nm in diameter are achieved through sonication and stabilization procedures. The presence of both the epoxy resin and solvent core components is confirmed by differential scanning calorimetry, (DSC) measurements, and the relative amount of epoxy and solvent in the liquid core is determined by thermogravimetric analysis (TGA). The capsules are shown to satisfy the requirements for use in self-healing materials including processing survivability, thermal stability, and efficient in situ rupture for delivery of healing agent. (C) 2008 Elsevier Ltd. All rights reserved.