Abstract
Recent high-performance sports shoes sometimes have a sole which made from several materials composed of different properties.
One of such material is foaming rubber. This is produced by foaming a rubber, cut with a mold, then pasted to a sole.
As this foaming rubber-contained sole causes conspicuous differences in a process of manufacturing, there is no identical sole even if the shoe is of the same size.
This intrinsic distinction could be extremely effective in differentiating diversities.
