Microcellular casual footwear sole

Microcellular polyurethane sole is the most common sole type in casual, safety, executive and utility footwear. The process uses a bicomponent PU system (polyol + isocyanate) injected into a closed mold — the mold may have the shape of the complete sole (for footwear where the sole is a single piece) or may be injected directly onto the already-assembled upper (direct attach).

The microcellular structure — with cells of 50 to 200 micrometers — results from specific formulation with internal blowing agents (typically water reacting with isocyanate generating CO₂) and mold temperature. This microcellular structure is what gives the PU sole its characteristic properties: lightness (density 0.4 to 0.8 g/cm³), flexibility, abrasion resistance, impact absorption capacity and excellent adhesion to various surface finishes.

Dual density systems (with a harder external layer for abrasion resistance and a softer internal layer for comfort) are manufactured through two consecutive injection processes. PU integral skin produces soles with smooth and dense surface skin and lightweight cellular core — popular in women's and fashion footwear.