The spirit 4 and Tornado are the same plastic - PU, the spirit 3 is Pebax, hence it's softer and lighter.
Acording to local shops (Cham) and messing with my buddies boots. The Tornado is no stiffer than my Spirit 4's, just more alpine binding freindly. It is missing the Dynafit fitings and the sole is not so hot for scrambling. It is much more popular here because it hit the streets a year earlier.
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