Terms to know when buying boots:
liner and shell: A ski boot has two parts, a plastic shell and a squishy liner. The liner serves to hold the foot stable inside the shell, and provides insulation so the foot won't suffer from the cold.
pack out: Liners are somewhat elastic. They mold to the skier's foot to fill the gaps between the foot and the shell. They get squished thin and stay thin in the places where they are pressed continually against the shell. Almost all liners provided with boots pack out. In an ideal world, the boot would be too tight at first (but not insufferably so) so that when the liner packs out the boot fits perfectly.
comfort fit: This is the fit a buyer gets when the buyer says comfort matters more than anything. The buyer often ends up with boots two sizes too big, which feel great in the store but will soon feel sloppy on the feet when the liners pack out. Such skiers will end up wearing two pairs of thick socks eventually, which don't solve the problem because socks are squishy and move around. They may seek help getting their boots to fit later in a shop. Bootfitters will glue shims to the outside of the liners in an attempt to stabilize the feet inside the boots. Often skiers end up buying another new boot that is one or two sizes smaller when the bootfitter tells them they can't fix the problem.
performance fit: This is when the buyer convinces the bootfitter that the boots should enhance the skis' performance. Bootfitters who have gone through training are capable of doing a performance fit, but not shop workers who have learned on the job over a short period of time working there. This fit will feel unusually tight in the shop, and causes buyers who are unfamiliar with performance fitted boots to think the boots are too tight. The bootfitter chooses a size that is quite snug in all three dimensions, length, width, and height, then grinds indentations into the shell, or punches outward bulges in the shell, to make room for bony bumps on the feet. Skiers choosing a performance fit need to wear very thin socks, not only in the shop but on the slopes. The liners should keep their feet warm. Thick socks will make a performance fit impossible to get into.
recreational fit: This is the fit that's half way between a performance fit and a comfort fit. When the liner packs out, the boot will allow the foot to move a bit inside and the skis will wobble as a result. Often skiers resort to thicker socks and/or thick shims glued by bootfitters to the liners (for a fee) to help keep the foot stable and get the skis under control.
shell fit: This is when the bootfitter takes the liner out of the shell and has the buyer step into the boot to check how much room is in there for the liner to take up. This step in bootfitting allows the bootfitter to choose a boot that will match the anatomy of the buyer's feet lengthwise, widthwise, and heightwise. Bootfitters may skip this step if they profile a skier as wanting a comfort fit.
grinding and punching: This is what a certified bootfitter does to make room in the shell for bony protrusions on the feet. This is not necessary with a comfort fit, and sometimes not needed for a recreational fit. It is often necessary for a performance fit, and should be free. Buyers usually can return to the shop for more adjustments of this sort for the first year after purchasing, and these adjustments also should be free. The need for such adjustments doesn't show up clearly until the skier has skied the boots for a while.
cuff canting or cuff alignment: The bootfitter will adjust the cuff so its tilt lines up with the lower leg's tilt, if the boot permits. This is free.
boot sole canting: The bootfitter, for a fee, may suggest adding wedges to the inside or outside of the boot soles. This is needed if the skier is very knock-kneed or very bow-legged, or if the skier is seeking high performance from the boots. The purpose of wedges is to help the skier keep both skis at the same edge angle to the snow.
aftermarket or custom footbed: The footbed provided with boots is flat. There is no arch support nor heel support. An aftermarket footbed can provide these supports if it matches the anatomy of the foot. Custom footbeds match each foot exactly. The purpose of such footbeds is to keep the foot securely in place in the bottom of the boot and to stop the foot from rolling left-right. They can help eliminate foot fatigue and foot pain if the buyer is prone to such things.
boot heaters and chemical toe warmers: These are what skiers with naturally cold feet use to keep their feet warm. Thick socks do not work very well.
thin socks: All skiers should wear the thinnest socks they own when buying new boots. Yes, some people even go so far as to wear compression socks or socks that fit like tights.
