Whenever a bootfitter slips what he or she knows to be the correct size on a prospective customer, it's standard procedure to intone, "You will feel your toes at the end of the boot; please try not to panic," or some such admonition.  This caveat applies in nearly every instance because the foot in an unbuckled boot will always seek the toe-bending end; only after buckling and flexing will the tootsies retreat into a less confining space.

The bones in the green zone should be the focus of every fit.

This "toes will touch" moment is, for many skiers, their first intersection with a concept we at realskiers have adopted as our own, "Fit Tension."  This particular term of art we first heard from the lips of Jim Schaffner, an undisputed master of optimizing equipment who plies his trade at Start Haus, the store he grew from cottage industry roots in Truckee, California.

Every individual has a tolerance level for fit tension.  Racers learn early on that they must learn to live with their feet in close confinement if they want to stay in the hunt.  While there's no reason for recreational skiers to endure the sustained pressure of a race fit, anyone can benefit from learning where they should feel high fit tension and where it can be relaxed.

The legendary Salomon SX 90. The highlighted area indicates the path of the interior HIP cable.

The most critical fit area in a ski boot follows a circumference Salomon once christened the heel-instep perimeter (HIP), a zone that encircles the ankle.  This is where fit tension should be so snug that it feels as though the liner is penetrating space previously occupied by skin.

Another way to describe where fit tension should be highest is to consider the shaft of the lower leg, down to the heel, as a steering column. The closer the shell and cuff can be brought to the steering column, the better the cuff will wrap around the skier's lower leg and the more secure the connection will be between skier, liner and shell.

Note that we don't talk about fit tension across the forefoot, even though forefoot width is the key metric in every boot's last shape.  (Hence the terms "98mm liner" or "100mm last.")  The forefoot needs a subtle range of motion to function inside a ski boot, a ROM that can be shut down if fit tension is too high.

Fortunately, expanding a boot anywhere across the metatarsal ridge is a piece of cake, so, if the only place a shell exerts intolerable fit tension is just behind your toes, this extra pressure can easily be alleviated without compromising desirable high fit tension around the heel.

Knowing the importance of proper fitting, K2 won't allow their boots to be sold on the Internet.

No one, from racers to never-evers, can ski at full potential in an oversized boot. This is why the "toes will touch" moment is so important; the boot customer has to endure a flash of fit tension in the toes in order to achieve and maintain essential fit tension at the heel. While toes need just enough room to wiggle, any extra room lengthwise will allow the foot to slide forward once this whole operation is set is motion.  If steering is shot, control is kaput and confidence quickly corrodes.
 
The lesson, Dear Reader, is to listen to your bootfitter as he coaches you into your first new pair of boots in several seasons.  Realize that the new boots are as unfamiliar with you are you are with them; they need a few minutes to relax their initial tension and get to know you.  You need to do your part by buckling down and flexing forward until your toes just brush the end when your ankles and knees are flexed.
 
Many skiers suffer unnecessarily because they believe that a comfortable ski boot is an oxymoron.  In today's era of custom molded components, it's lunacy to continue to ski in pain, or even mild discomfort.  To achieve the best all-day fit, start with a boot that imparts a sensation of immediate, intimate contact everywhere; the intensity of its first embrace will evolve, in short order, into a comfortable conformity that is made to last for years. 

Thanks to Jackson Hogen and realskiers.com for this article.