The Nordica Women's Transfire R4 All Mountain Ski Boots are a brand new boot that expands on Nordica's award-winning Firearrow performance shell design with the introduction of all new top performance features demanded by modern skiing, yet in a package specifically tuned for those skiers who are less confident and not as precise in their movements from edge to edge. The new Transfire boots are specifically tuned for the advancing recreational skier by allowing for easier handling and a more comfortable stance. 102mm last. Instead of just one number representing the flex, Nordica has adopted the Dynamic Performance Code to measure three performance parameters. Stiffness (1-20) measures the amount of force needed to bend the boot forward. Progression (1-3) is how much stiffer the boot gets as it is flexed forward. Rebound (M=slow, H=medium, E=fastest) is how quickly the boot returns to neutral from its deepest flex. The stiffer the boot, the higher the transmission of power to the ski.The R4 has a flex rating of 12.0. The bigger progression, the stiffer the boot behaves through the forward flex allowing the most precise load transmission of the ski. The R4 has a medium progression rating of 2. The higher the rate of rebound the faster the boot returns, enabling a quicker turn and ski edge change. The R4 also has a slower rebound rating of M.