Core materials include end-grain balsa wood, PVC foam, urethane foam, non-woven core textiles, and a variety of honeycomb materials. Sandwiched between two composite skins, these lightweight materials are the main component of a "sandwich construction."
The flowability of the core materials is an important factor in successful healing. Before the agent is consolidated, the core material should flow out of the fractured microcapsule and quickly into the crack plane. Sun et al. employed laser microdissection to cut the microcapsules and microscopic imaging to assess flowability. When the shell was damaged by the UV laser, the rejuvenator spilled out of it and swiftly spread around the area. It took only 10 seconds for 55 percent of the rejuvenator to leak out of the cracked shell.
