Found this on alpinecarving.com, but it still sounds incredibly complicated to me ... and this seems to be aimed at Raichle boots. I don't know.
Here are the unabridged instructions for heat molding liners. After molding the liner at a bootfitter, make sure you get a bag containing all the boot fitting paraphernalia that was used (foam patches, etc) so that if you wind up needing another molding, you can bring back all the stuff and resume from a known starting point. You can re-mold the liners up to 6 times (and probably even more than that). Every time you heat mold the liners, the liners shrink a little bit, they get a little stiffer, and it takes a little more heat to do the job. The HPD Thermoflex liner is thicker, stiffer, and for the same size will take up more space than either the regular Thermoflex liner or the Intuition liner. If you have weird shaped feet, or need to fill a lot of volume around a skinny ankle, go with the HPD liner.
In the past, some Thermoflex liners came with plastic pieces, which were meant to be put over the liner instep, to prevent the shell from pinching the liner.
The inside sole base of each boot shell usually has a ribbed plastic structure for greater rigidity. You must make sure that this ribbed structure is covered with the thin plastic sole cover that comes with the boot, otherwise the liner will warp in the wrong way as it molds.
Prevent the liner from tearing by covering sharp areas inside the shell with duct tape.
Find a bootfitter who has a convection oven that circulates air to avoid hot spots. It can be any convection oven - it doesn't have to be the official Raichle oven.
Put the liners in the oven at 200º-250º F for 12-13 minutes, with the liners upright, facing you. Do not use hot air hoses to mold the liners.
If you have any sensitive areas on your foot that could result in rubbing/pressure problems, cut out a 1/8" thick foam adhesive patch and stick it directly on your foot: The patch will create extra room in the liner. Be sure to bevel the patch at the edges.
If you are using Intec heels, make sure the cable is in place, and tape it to the shell so that the liner molds around the cable.
If you have a footbed, hold it on the bottom of your bare foot.
Then place a toe cap over your toes and the footbed. The toe cap provides room in the liner for your toes so they don't get crowded. Raichle ovens come with neoprene toe caps of various sizes (small, medium, large). However, if you don't have one, you can make one by cutting the top off of a thick woolly sock: The cap should cover your toes and come down to the ball of your foot. As an alternative to using a toe cap, you can wiggle your toes like crazy while the liner cools, but this method is not recommended. If you need a lot of extra space in the toe box, you can put bootfitter's foam between your toes. It's not important for your toes to have a tight fit, since you will be balancing on the ball of your foot.
Put on a tight thin ski sock so that it holds the toe cap and footbed in place. Make sure there are no wrinkles in the sock. You need a tight sock to keep the footbed and toe cap from shifting around.
The liner will be hot enough when it has a jelly consistency.
Take the liner out of the oven and wrap it around your foot like a burrito. Then sit down and stick your foot out horizontally so that the bootfitter can shift the liner around so that the seam on the bottom of the liner sole goes exactly down the center of your foot.
Stand up in the liner and pull up gently on the liner cuff to make sure your foot is all the way in. Then put your foot (with the liner) into the shell while someone holds the boot shell open for you (it's a two-man job). When heat molding Intuition liners, It is recommended that you put a grocery store bag over the liner before you insert it into the shell - otherwise, the liner can catch on the inside of the shell and get squashed. This problem does not seem to happen with Thermoflex liners.
If you are having problems with wrinkles in the liner, have the bootfitter hold down the shell, and lift your heel and the liner up about 1 inch. Then while pulling gently up on the liner, push the liner back down into the shell with your foot. Don't pull too hard, otherwise the liner may get stretched and extend far above the shell.
Before you tighten the buckles, you can compress the liner around the cuff a little to keep it from sticking too far above the cuff.
Tighten the buckles half-tight, so that the liner just molds to your foot. If you tighten the buckles less, you will get a tighter fit after the liner cools. If you tighten the buckles more, you will get a looser fit.
Hit your heel on the floor several times, and flex a few times, to get your foot into the heel pocket of the boot.
The boot will feel looser as the liners cool, but do not tighten the buckles any further during the cooling process.
Do the process with the other foot. Then Wait 10 minutes while standing with your toe elevated about 1.5 inches above your heel to make sure that you correctly mold the heel pocket - a shop will use a bootfitter's angled platform. Make sure you have even weight in both boots: don't cock your foot side to side. Then stay in the boots for another 10 minutes until the liner cools completely.
If there are still some pressure points or rubbing, you can heat gun the liner and then crush it in a press. The liner can be compressed down to 1/8" thickness.
You can also heat mold the liners in a non-convection kitchen oven. Preheat the oven to 250º F, put the liners in the middle of the oven, then turn off the oven to prevent scorching, and cook the liners for 10 minutes.
For people who ask "Can I just do it myself?": If you have seen a bootfitter go through the process of heat molding the liners, you are probably clueful enough to do it yourself in your own oven. Otherwise, it's going to take a quantum leap of common sense to get it right.
Normally, convection oven molding followed by heat gun tweaking is supposed to provide a perfect fit with no additional bootfitting needed. However, some carvers still need major adjustments, like punching out the shell or adding/removing liner material.