Insoles come in different volumes, which means that they take up different amounts of space inside your footwear. For most insoles, there is also a correlation between volume and the arch shape that the insole is designed to fit.
High-volume insoles best suit high-volume shoes such as hiking boots, ski boots or running shoes. They typically work best with high arches.
Medium-volume insoles fit average-volume shoes, like casual shoes and some athletic footwear. They work well with a variety of arch profiles.
Low-volume insoles are needed for low-volume shoes such as a cycling shoes, in-line skate boots or ski skate boots. People with very low arches often find a low-volume insole works best for them.
(Note: The thickness of your socks will also have a big influence on footwear fit.)