Method of customizing a boot

A kit for customizing a thermoformable boot, comprising:

• a re-usable core dimensioned to generally correspond to a foot size of the thermoformable boot, the re-usable core selected from a group of re-usable cores each corresponding to a different range of standardized foot sizes;
• a sacrificial medial side insert manufactured based on a tridimensional shape of a wearer’s foot, the sacrificial medial side insert having a medial internal surface and a medial external surface generally conforming to a medial side shape of the wearer’s foot;
• and
• a sacrificial lateral side insert manufactured based on the tridimensional shape of the wearer’s foot, the sacrificial lateral side insert having a lateral internal surface and a lateral external surface generally conforming to a lateral side shape of the wearer’s foot;
• wherein the sacrificial medial side insert and the sacrificial lateral side insert are insertable into the boot with the selected re-usable core having a foot size generally corresponding to a foot size of the boot, the medial internal surface and the lateral internal surface abutting outer surfaces of the re-usable core.