From the Superfeet Website
The volume generally associates itself with the shape of the foot. For instance, if you have a high volume foot: this would be a foot that has a very wide forefoot across the ball of the foot, a very wide heel, and a high instep (which is the top of the foot).
A low volume foot would be considered a very narrow, skinny foot that would have a very narrow forefoot, and an instep on top of the foot that is a little bit lower in its height, but not necessarily flat. It would also be associated with a very narrow heel area.
You can have a high volume foot with a high arch, or you can have a high volume foot with a flat arch. You can have a low volume foot with a high arch, or you can have a low volume foot with a flat arch.
The volume of the foot does not necessarily associate itself with the height and shape of the arch on the bottom of the foot.
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"...I'm like the cycling version of the guy in Flowers for Algernon." Mike Magnuson