The ballons do not make the glue stronger, the makes the glue more flexable. I use them in the ski industry to fix blown edges and sidewalls. Allows for filling holes without have a solid piece of glass in the hole.
If a solid piece of epoxy is frozen and hits with a rock it will shatter. The ballons stop this effect by allowing a tiny bit of flexablity.
Heat helps flow the mixture.
I mix alot in until the epoxy almost rejects taking any more in.