UNDERSTANDING "LAST WIDTH" CATEGORIES AND FIT TENSION MEASUREMENTS
So what about this 98mm, 100-102mm, 103mm and up stuff? Well, these are width measurements that boot companies use to describe a boot in a particular width category, like narrow, medium, and wide. It’s an industry-wide attempt to provide a numeric rating for width—sort of the way a flex index number tells you how stiff the boot is. And similar to flex index, the metric last width measurement (so-called due to the "last" or boot mold) can be a little variable, but all in all it’s a good thing for consumers and bootfitters alike. So long as you’re savvy to a couple important points!
Most importantly, this number refers only to the measurement taken at the widest part of the boot shell’s forefoot, internally, and only in the reference size 26 (that’s a U.S. men’s 8, women’s 9).
Taking out a digital caliper tool and measuring your forefoot would be a waste of time for the most part—even if you were a size 26— because the last width measurement doesn’t take into consideration the liner fit, so it’s just tough to use the last width measurement number as anything other than a name for the width neighborhood a skier tends to hang out in, so to speak. But that’s reason enough to keep this number system. It works on a couple different levels, not just for width but also for what we call fit tension.
Fit tension is essentially how snug a boot fits — and that’s dependent on both the volume of the boot and the volume of the foot. For example, take a fat foot and stuff it into a narrow last boot and you’ve got yourself some serious fit tension, baby. But keep in mind that a skier’s ideal fit tension is a subjective thing — some skiers can handle a lot of compression, others not so much. But note that it is not always the case that wide feet find themselves in wide category boots. In fact, most of our testers with medium width feet use narrow category boots for their personal use (with some bootfitting) in order to get the sort of tight fit they like for high performance skiing. You will find our Fit Tension Rating (FTR) in each boot’s fit impressions table — this score is a simple average of all the fit parameter scores and provides a rough idea of where the boot falls relative others in terms of its fit tension
Article from ABB - Masterfit
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