Boot fit is an important factor in determining comfort and performance while skiing or snowboarding. A close, comfortable fit helps the boots feel like an extension of your body, and gives you more control over movement. Thermoflex liners, also known as heat mouldable liners, are used as a method of fitting ski and snowboard boots to achieve a customised fit .The liners are heated, making the material flexible and pliable enough to be moulded around a foot. When the liner cools it retains the custom shape. Many boot shops can fit the liners for you, but if you are at home the process can be completed using a convection oven.
Remove the liners from you ski boots. The liner is the inner layer of the hard outer shell portion of the boot. When you are looking at the boot, the liner is typically the second layer from the outside of the boot. It is made primarily of a thin plastic and has a plush interior. The colour of the liner varies depending upon the make and model of the boot.
Remove the foot bed from the bottom of the liner. The foot bed easily pulls out of the boot. The process is just like removing an insole from a tennis shoe. Pull out any laces if they are present. The foot bed and laces may melt to the liner if they are left in the liner during the moulding process.
Remove the top rack from your oven. This will give you plenty of room to safely insert the liners.
Preheat the oven to 135 degrees Celsius on the convection setting.
Line a baking tray with tinfoil. The tinfoil creates a safe surface on which to place the liners while they are in the oven.
Set the liners on the baking tray. Place the liners upright on the baking tray, side by side. Place the baking tray in the centre of the rack in the oven.
Prepare yourself to mould the liners. Do one liner at a time. Put the foot bed you will be using with the liner under your foot and place your toe cap over the top of your toes. A toe cap is a foam cap that protects your toes by preventing them from jamming against the top of the liner. If you do not use a toe cap, you can use a thin sock or stocking to hold the liner on your foot during the moulding process. If you wear socks while wearing your boots, you should put on a sock that is similar to the ones you wear while skiing or snowboarding to ensure that the mould you create is most like the one you will need on the slopes.
Remove one liner from the oven after 10--15 minutes of heating. The liner should appear larger and slightly more inflated than usual. Use caution so that you do not burn your skin. Oven gloves can protect your hands but you may find them cumbersome. Wearing gardening gloves provides a protective layer without being overly cumbersome. Put the liner onto your foot, making sure that your heel is firmly against the back of the liner. Pull the front and back of the liner together with your hands so that the sides overlap slightly. The front of the boot should tuck under the back portion of the liner like the lounge of a tennis shoe. The liner should feel snug around your foot and ankle.
Insert your foot with the liner into the outer shell of the boot. Make sure that the liner is in the boot straight, with no folds or wrinkles in the surface of the liner. Buckle the outer shell of the boot as you normally would during use. Keep in mind that the tighter you buckle the shell, the looser then liner will fit after the moulding process. This is because the mould is being fit by pressure and will take up less room in the boot. The more pressure you place on the mould during the fitting, the looser the boot will fit following the fitting. If you are worried that the boot will fit too loosely you may want to initially buckle the boots half as snugly as you normally would.
Remove the other liner from the oven and repeat Steps 7 and 8.
Stand in a neutral snowboarding stance or skiing stance, slightly flexed forward, for approximately 10 minutes as the moulds cool. Your feet should be flat on the ground.
Remove everything from your feet. Inspect the completed mould. Make sure that there are no folds or creases along the surface of the liner. Place the liner in the boot shell and place the foot bed inside the liner.
Slide your feet into the fully assembled boots to ensure that the moulds are properly fitted. Most brands of heat mouldable liners can be remoulded up to five times.
Wear oven gloves or gardening gloves to protect your hands while working with the heated liners.