The flex of a ski boot is the measure of force required to bend the boot at the ankle. The stiffer the boot is, the more support it provides. A stiffer boot requires the skier to stand with their weight further forward in order to transfer energy through the boot to the ski effectively. Softer, more forgiving boots are meant for less experienced or lighter skiers. A softer boot requires less energy to initiate the turn of the ski. 

Ski boot flex ranges from about 40 (for small children) up to 130 for general consumer boots. An 85 flex is generally a medium stiffness for intermediate women skiers, and a 100 flex is a generally a medium stiffness for intermediate men. Some race boots, categorized as “world cup flex” are measured at 140-170 flex and are built for only the most aggressive skiers. Ultimately, the flex index is not a perfectly succinct measurement across boot brands; it is always best to try a boot on before buying to confirm the flex works well for you. 

The last of a ski boot is essentially the width measurement of the boot shell at the forefoot. The last is also a general indication of the volume inside the boot shell; a wider last increases the boot’s overall volume. A boot with a narrow last is generally measured at 97mm or 98mm wide. A medium last measurement is about 99mm - 101mm, and a wide last is any measurement 102mm or greater. 

In recent years, many manufacturers have started building liners that can be custom molded to the skier’s foot using a specialized oven. The liner is heated to soften the inner foam and inserted into the boot shell. The skier then inserts their foot, tightens the buckles and stands in the boots while the liners cool and form to their feet. A heat moldable liner allows for greater fit customization for the skier and ultimately more comfort. 

**The liner molding process should always be performed by a qualified boot-fitter with the proper tools. Trying this at home could damage your liners. **

Modern touring bindings have been engineered to attach differently than a traditional alpine binding. The “Tech” style binding uses pins that fit into specific inserts in the sides of the boot’s toe and into the back of the boot’s heel. These special inserts are built into the boot and are necessary to utilize a tech style touring binding. 

Some boots feature replaceable soles in the form of plastic plates that screw on and off the sole of the boot. Replaceable soles prolong the life of the boots once they’ve experienced lots of wear from walking on non-snow surfaces. 

Most modern boots have buckles with micro-adjustability features built in. Buckles screw in and out to lengthen or shorten the reach. This feature is useful when you need a bit more tightness but don’t need to go to the next ring on the buckle.