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Thermoplastic elastomer foam is often used as a midsole, which is an important factor affecting sports efficiency. In this research, ethylene vinyl acetate copolymer/polyolefin elastomer/styrene ethylene butylene styrene (EVA/POE/SEBS) microcellular foam was prepared with supercritical nitrogen gas (SC-N2). The influence of the formulation ratio on the matrix network structure was studied by vulcanization curve and rheometric expansion system rheometer. Then the foaming behavior and static/dynamic mechanical properties were studied, and midsole was prepared. The results showed that the increase of the relative content of SEBS reduced the viscosity of the matrix, but the loss factor increased, which further reduced the resistance to cell growth and increased the expansion ratio (density decreased from 0.19 to 0.13 g/cm3). In addition, the increase of SEBS resulted in an increase in the static compressive strength and resilience (61%) of the foam. However, after 100 000 dynamic compression cycles, the increase of SEBS resulted in a decrease in the energy absorption capacity of the foam and an increase in the dynamic compression set (from 6.8 to 9.4%). This is significantly different from the traditional physical and mechanical performance test results, which are rarely reported and have significance for practical applications.

Expanded thermoplastic polyurethane (ETPU) foam materials with superelasticity for footwear application were developed and investigated. ETPU foams with different ratios of CO2/N2 as foaming agents and ETPU foams prepared by pure nitrogen foaming with different kinds of foaming additives were prepared by supercritical (Sc) foaming technology, which further made into sheet forms through the steam molding process. TPU foam exhibits better cell structure, crystallization performance, and mechanical strength with the increased CO2 proportion. Further, the foams using 25% CO2–75% N2 and 50% CO2–50% N2, showed a lower density and excellent resilience and cyclic-compression performance. However, an increase of N2 ratio improves the dimensional stability and compression set of the foam. The introduction of foaming aids enhances the interaction between Sc-N2 and TPU. The ETPU foam prepared under the same conditions has a smaller density and a larger expansion ratio. Especially the ETPU foam prepared by Sc-N2 using monofluorodichloroethane as the foaming assistant as a co-blowing agent, the decrease in cell size (from 117.9 to 19.6 μm) and density (from 0.175 to 0.139 g/cm3) has observed. The study revealed the high potential of these materials in footwear applications and offered sound evidence for mass production in the industry.