Some running shoe brands are using nitrogen infused into the foam midsole by process dubbed “supercritical fluid foaming” which produces a softer and lighter foam. These include, for example, Puma (eg Deviate Nitro), Brooks (eg Aurora-BL, Glycerin, Caldera) and McLaren (APL McLaren HySpeed).
During the manufacture of the foam, heat and pressure are applied and liquid nitrogen is included. When enough heat and pressure are applied, the liquid nitrogen starts converting from liquid to a gaseous stage. In the middle of that transformation is that supercritical state. When this supercritical state is achieved, the material is injected directly into the foam and held there for a certain amount of time. The heat and pressure is then lowered and the nitrogen infusion is claimed to magnify the foam’s qualities of softness and responsiveness.
Promotional explanation of the nitrogen infused midsole from Brooks by Dr Raven:
The process is subject to litigation with Puma filing this suit against Brooks in August 2022 with Puma claiming that the design of the Brooks shoes is covered by their patent and Brooks have infringed upon it. Puma are also alleging misuse of the ‘Nitro’ branding that they own the trademark for.
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