Closed cells
By Expancel microspheres
Every little particle is a separate sphere or cell - it is a microsphere. The cells are closed, and therefore expandable. If they had not been closed, they would not be able to expand. Closed cells maintain the gas and do not absorb water, which is a benefit in e.g. insulation and injection molded shoe soles. Using Expancel to add volume to a matrix - you are in complete control of the added volume.