The average person takes 5,000 to 10,000 steps per day. Each step subjects the foot to forces several times body weight. The shoe sole that cushions these forces is a marvel of engineering—and at its core is Microcellular foam . This lightweight material, filled with millions of tiny gas bubbles, provides shock absorption and energy return that solid rubber cannot match. But foam alone is not enough; the sole also needs a tough, abrasion-resistant outer layer. That is where Polyurethane elastomers excel. Together, microcellular foam and polyurethane elastomers create soles that are light, durable, and comfortable—qualities that every shoe wearer demands.

The Microcellular Foam Advantage

Microcellular foam is defined by its cell size: typically 10-100 micrometers in diameter, compared to 100-500 micrometers for conventional foams. This smaller cell size provides several performance benefits:

• Higher strength-to-weight ratio – Thinner cell walls provide the same strength with less material

• Better fatigue resistance – Small cells distribute stress more evenly, reducing cracking

• Smoother surface finish – Fine cells do not telegraph through thin outer layers

• Lower thermal conductivity – More cell walls block heat transfer

The Microcellular foam market produces foams through several processes:

Chemical foaming – A chemical blowing agent (often water or azodicarbonamide) decomposes during polymerization, releasing gas that forms cells. This process is simple and cost-effective.

Physical foaming – Nitrogen or carbon dioxide is dissolved into the polyol under high pressure. When pressure is released during dispensing, gas comes out of solution, nucleating cells. Physical foaming produces finer, more uniform cells.

Supercritical fluid foaming – CO2 or N2 is brought to supercritical conditions (above critical temperature and pressure), then dissolved into the polymer. Upon pressure release, extremely fine cells (5-20 micrometers) are formed. This is the premium process for high-performance athletic footwear.

The Microcellular foam market has seen a shift toward physical and supercritical foaming as athletic brands demand better performance and consistency.

Polyurethane Elastomers for Wear Surfaces

While foam provides cushioning, the ground-contact surface requires a different set of properties. Polyurethane elastomers used for outsoles are formulated as solid (non-foamed) materials with:

• Hardness – 60-95 Shore A (softer than rubber but harder than foam)

• Abrasion loss – <50 mm³ (DIN abrasion test), comparable to premium rubber

• Tear strength – >40 N/mm, resisting cuts from sharp rocks or debris

• Coefficient of friction – 0.6-1.0 on dry surfaces, 0.4-0.7 on wet surfaces

The Polyurethane elastomers market offers both polyester-based and polyether-based formulations. Polyester elastomers have better abrasion resistance and higher strength; polyether elastomers have superior hydrolytic stability (resistance to degradation from water and sweat) and flexibility at low temperatures. Most athletic shoes use polyether elastomers for the outsole; work boots may use polyester for maximum abrasion resistance.