Ski boot buying can be a daunting, and often put off, process that may involve many trips to the ski shop or local bootfitter plus time for heat molding and tweaking during everybody's favorite break-in period. Going into the process knowing what type of boot you need for how and where you ski is where a new boot search begins, but fine-tuning your search by last-width and stiffness can fast-track your journey toward your best boot match.  

Last (width)

Narrow, medium or wide—some skiers' foot shapes make those decisions obvious. Other feet can be either more or less tolerant of compression, or fit tension, and so skiers may trend away from what their foot shapes might suggest and toward narrower boots for a more snug fit or wider boots to avoid chronic numbness and promote warmth. 

First, the numbers. The so-called last width measurement is the distance, in millimeters, taken from the inside of the shell at the widest point of the forefoot on only the reference size 26/26.5 boot in a given model. Narrows fall into a range between 96-99mm. Medium lasts are considered 100-101mm. Ski boots are considered wide at 102mm and up.    

Don't know where you fall? Don't reach for a digital micrometer; just get to a good shop and ask to try on some boots—you'll learn pretty quickly what width neighborhood to call home. Do ski boots fit the way the manufacturer says they do? Not all. It's why we test 'em… our reviews won't steer you wrong. 

Stiffness (flex index)

The so-called flex index is a number assigned to a boot that conveys how stiff that boot is in forward flex (the feel against your shin). The higher the number, the stiffer the flex feel.

In our boot test this year, the softest boots we tested were 80s and the stiffest were 140s. How do skiers decide what flex is best? Usually through trial and error, but with some guiding parameters: A boot needs to be stiff enough to support the skier's tall, neutral stance—the too-soft boot will collapse under the weight and leverage of the skier, creating too much bend in the knee and resulting in smoking quads. Conversely the too-stiff boot won't budge under a skier's typical flexing pressure, rendering a skier's movements overly static and causing sore shins.

As with skis, stiffer boots transmit edging movements more effectively, enabling stronger carves and more stability at speed on harder snow. Softer boots are more forgiving and soft to the edge so better for those lower on the learning curve. While huge strides have been made in recent years with respect to easing entry and exit, as a general rule, softer boots will be easier to get on and off. Due to the costs associated with materials and construction, the stiffer the boot, the higher the price.