Compared to other materials, Superfeet Kork are pretty thick underfoot, and often do reduce boot volume. The old Superfeet SkiVac has no kork is thinner, and very worth considering, as are lots of other footbeds; Comformable, Instaprint, Etc... I have a very snug fit in my boots, and the Superfeet rep made me a pair of Korks last year, trying to convert me. They are much thicker than my Instaprints, and did not work at all. Maybe if I neede volume reduction... There are quite a few people who find Superfeet's nonKork footbeds preferable to a Kork, including one Demo team guy I work with.