Expandable microspheres are white microscopic
spheres (with an average particle size of 10~30 μm and an average density of
approximately 1100 kg/m3) that comprise a thermoplastic shell
encapsulating a low boiling point liquid hydrocarbon
When heated to a temperature high enough to soften the shell, the increasing pressure of the hydrocarbon will cause the microsphere to expand by 40 to 100 times. The microsphere ceases to expand when its inner pressure, shell tension and external pressure reach a balance. Its density after expansion can be lower than 30 kg/m3（0.03 g/cm3), making it one of the most lightweight application materials in the world.