I bought these as replacement for the standard footbed that comes with ski boots (ski coach recommends this practice). Customization was easy - scissors to trim to size (helps if you take the boot liner out), then heat in the oven for 2 mins, insert and wear the liners for 15 mins or so. Right away you can feel the increase heel support and underfoot support as the insole forms to your feet. I'm still waiting for snow to try these out, but they do give you a more custom fit. Since these are heat fit, they will work great for new boots with heat customization boot liners - do both at the same time. Also consider Shock Doctor insoles - they also have good heel and overall support - stiffer base.