The Sidas Thermo CRT liner is a 100% thermoformable, moldable ski boot liner. What does all that mean? It means you get a liner that is completely customized to the shape of your foot for the ultimate in comfort and performance. The Thermo CRT was developed in France over 2 years with some of the best boot fitters in the world. Utilizes varying thicknesses in key areas, the liner provides the perfect blend of support and cushioning once moulded to your lower limb.  These liners are great to rejuvenate an old pair of ski boots when the shells are in great condition and the liners have packed out. They'll be lighter and warmer than most stock ski boot liners too. Complete with laces and a flex zone on the calf, we personally use this liner in our backcountry ski boots with great success. It is definitely recommended to use a custom footbed with this liner and at the very least a pre-fabricated insole. Even after being moulded by your boot fitter the liners can take a few days to break in, but once they do look out. Sidas Thermo CRT Custom Ski Boot Liner