Two feet of the same size can have very different instep heights. Among men's US 9 feet in our scan data, the gap between the 10th and 90th percentile instep height at 55 percent of foot length is more than 12 mm. Laces have been the default way that footwear absorbs that spread, for literally thousands of years. But it's clear from the data that achieving the best tension across the various zones of the top of the foot is difficult to do consistently with that solution.
Zipzōn, a Colorado-based company that develops integrated fit systems for footwear brands, builds a zonal fit system that effectively replaces laces. The system closes across specific regions of the foot rather than pulling the whole foot down at once. To design it, the team needed to know what those regions look like, not on one foot or ten, but across the full range of feet that will wear the shoes it goes into.
For each US size in the study, we calculated instep height at seven positions along the foot, from 45 to 75 percent of foot length in 5 percent steps, measured from the heel. Together they trace the profile of the instep from just behind the ball to the point where the foot becomes ankle, as the vertical lines in the image show.
Instep height measured at 45 to 75 percent of foot length in 5 percent steps, shown on a random male US 9 foot from the study.
We reported three numbers at each position: the mean, the 10th percentile and the 90th percentile. The mean tells a designer where the typical foot sits. The percentiles tell the designer how far the low-instep and high-instep ends of the population sit from it. A system built to those two limits covers 80 percent of feet at every position along the instep.
Instep height has been measured before, but most studies measured it at one position only, typically at 50 or 55 percent of foot length. A system that closes across the whole instep needs the full profile, from the ball of the foot to where the foot turns into the leg, not a single point. With 3D scans, nobody has to be measured again: each additional position is a calculation on foot scans we already hold.
The values in this study come from Volumental's database of more than 85 million feet scanned in over 3,000 stores across 60 countries.
Zipzōn is using the numbers to build an adjustable 3D last model of its own, so the closure system can be checked against the full range of instep shapes before a single prototype is cut.
"I spent years at previous companies wishing we had solid data to build around," said Mike Nickel, Director of Product Development at zipzōn. "It's great to have access to it today, and this will help us make the installation process easier for our brand customers and ultimately the end user experience more comfortable and higher performance."
The output of this study is a spreadsheet and a set of plots. That is what data-driven fit development looks like most of the time: not a dramatic reveal, just the right numbers arriving before the design is locked.
The zipzōn project is one example of a pattern that we see quite frequently and often. Foot scan data collected at the point of sale has value far upstream of the sale, at the point where a product's fit is decided. Lasts, grading tables, size runs, closure systems and insoles are all designed against some idea of the foot. That idea can now be measured.
If your product team is working from averages, assumptions or a decades-old survey, we can tell you what your target population's feet actually look like, at whatever positions and percentiles the design needs. Read more about Data-Driven Footwear R&D, or get in touch.