Everything that burns has a pourous surface.  Because water has a high surface tension, plain water has a hard time soaking into some fuel sources.  Fire Cap Plus is a wetting agent that lowers the surface tension of water.  When a mixture of water and Fire Cap Plus is applied to these "hard to penetrate" fuel sources, the mixture is quickly absorbed, helping to reach the seat of the fire faster.  Because the water and Fire Cap Plus are actively penetrating the fuel rather than just sitting on top, the chances of a rekindle are minimized.  The diagrams below demonstrate the penetrating power of Fire Cap Plus.