The inserts have been designed to work with your custom insoles since we are aware of how much people love to use their own custom orthotics! They are ~2.5mm thin and should be placed between the liner and shell.
To install, you remove your entire liner from your ski boot and stick the Carv insert onto your bootboard at the bottom of you boot with some attached sticky tabs. You then replace your liner.
If you order Carv and face any issues because you have particularly strange insoles, get in touch with us and we'll either work to resolve the issue or offer a full refund.