Sven's Sizing

The issue of SIZING has always been a perplexing problem. It is much better today, after a campaign I started forty years ago when I was accused of exaggerating the issue. In Berlin, circa 1973, I presented a Standardized sizing system at the first ISO/DIN Ski Equipment Safety meeting. It was simply the Japanese "metric" sizing and surprisingly everyone agreed, yet they ended up doing whatever suited them. Now the binding-adjustment sole length has been added as a vague sizing reference. To make the matter even more confusing, women's boot sizing is inconsistent at best and should always be stoichastically measured.

Why can the boot manufacturers state the "shell's" own internal equivalent foot size?
Maybe because -- they also refer to the sole length as the sizing reference?

Anyway, let's just use some simple shell measurements to help get you, the skier, into the proper Zipfit liner.


What I have recommended in the past is to use the measuring tape inside the shell. To do this, extend the tape into the boot as far as it can go into the toebox. Then by using your hand to push the tape deep into the heel cavity, it will curve up the back giving an internal shell length.

Typically, the Zipfit inner boot size is the same number as the shell's factory liner. To be sure use a metal measuring tape, push down to the toe end of the shell and bend the tape into the heel pocket.

BLUE lines show the middle of the tape bend and the internal shell size of 285 mm. This is also the external Zipfit length, allowing for materials.
WHITE lines show the Zipfit internal size of 275 mm, and the actual foot size within the Zipfit....


Fitting Particulars

When the shells are heated sufficiently (>110°C~230°F) the side panels and spoiler will thermally form to the shell and also adheres to the (black) outer lining. This reinforces and substantially increases all of your edging and flexing support. These are one of the unique new features presented by ZipFit presents to once again advance the state of the art in inner boot design, support, insulation & unprecedented comfort, sensitivity, performance & especially control.

THERMALLY MOLDABLE ANKLE PANELS: The side-panels are very thin and when the shell is heated, for initial fitting and molding, the heat transfers through the ankle reinforcing panels to thermally shape and mold to the shell’s internal plastic shape while bonding the adhesives to the outer lining material.

When cooled these panels boost the overall inner boot support and functional essence to enhance you with more leverage over the shell plastics and sensitivity over the skis. Therefore you need less closure tightness and have more amplitude in support and flex adjustability …and hence comfort. With normal liners tight buckling compresses the foam padding and constricts the feet, most often painfully.

The new Pro-Lacing and elastic tongue retainer system is very effective for wrapping the whole inner around the foot for the initial heat molding process. After molding the laces are optional.

The laces are most effective in creating additional and independent “soft-brace” foot-ankle and lower leg-shaft support within the stiff shells plastics. This, along with the inner boot shaft PowerStrap enables you to adjust the inner-boot independently of all the shell buckle adjustments; learning this gives you a much broader autonomy of adjustment and leverage over the shell for establishing the perfect flexing action and to ski with looser buckle settings. With this precise adjustment to your lower legs permits you to rely less on the shell buckle closures for support. It helps to make the shell plastic feel “transparent.”

Fitting Tips and Tricks


Rather than physically heating the liner, the paradigm Sven Coomer has been promoting for 30 years is to HEAT THE SHELL for all ski boot fitting. The heat transfers from the shell into the liner, your inner boot, which softens and enables the liner materials to adapt to both your foot and the shell. Both the shell and the liner adapt and shape to your feet, rather than forcing your feet to "break in" a cold shell and liner.

Heating the shell and your Zipfit inner boot for the initial fitting is a very simple and quick process, that only needs to be done once. It is also very important. 


Fitting the liners without heating shells for the initial fit takes longer because you are relying on body heat and dynamic activity. A cold Zipfit and shell can take a few days of skiing to adapt to your feet and provide maximum comfort and performance. That is why we strongly recommend you heat the shell for the initial fitting and for the first day of skiing in your new Zipfits. By heating them, there is no adaptation or adjustment period so they feel great from the first time you ski.


Ideally, after the initial fitting process, it is best to heat the shells once more just before you ski in your new Zipfits for the first time. That way, the OMFit composite in your Zipfits adapts perfectly to your personal anatomy and skiing dynamic. The liners will adapt within the first couple of runs (depending on how long the runs are).


With Zipfit you can heat the shells and liners every day ... the way the World Cup racers do ... with a Hot Gear Bag.

With a Hot Gear Bag, both the liners and the shells are completely dry and even the stiffest shells are very easy to put on. The Hot Gear Bag is another Zipfit invention to help people with very stiff and difficult-to-put-on shells. You can heat fit the shells (and Zipfit) every day for the best comfort and support with a Hot Gear Bag. This also activates the constant dynamic molding process of your Zipfit liners. The Hot Gear Bag allows you to use your Zipfit inner boot with any other boot shell - Nordic, alpine touring or alpine.

The Hot Gear Bag is considered to be an essential piece of every skier's equipment.


For initial fitting, many shops have a SKI BOOT CONVECTION OVEN specifically designed for heating both shells and liners that works wonderfully. (DO NOT use your kitchen oven, as temperatures can be inconsistent).

The next best alternative for heating the ski boot shells, and the most common practice, is BOILING WATER with a rice cooker, a tactic many pro shops have been using now for 30 years. The use of boiling water is a quicker process, and the temperature is finite, around 200 degrees.

Heating the Zipfit inner boots on a heat stack is fine, but it takes a long time for the hot air to penetrate the inner lining insulation materials and soften the composite. And the stacks of course do not heat the shells.

You DO NOT need to do this every day, but we encourage heating the shells on a periodic basis, because it will completely change any skier's experience.


While holding down the back of the shell step the other foot forward and genuflex your knee down to the floor. This motion spreads the shells stiff flaps and lifts the heel painlessly and effortlessly out of the shell. Be sure and leave your Zipfit fastened and on your foot during this process.

To put your Zipfit liner back in the boot, either heat the shell and/or use a friend to help open a room temperature shell.

Always "hoist" the liner to seat the heel under the heel huggers every day.

Racers and other experts have been going in and out of their boots this way for decades ... because of the stiff shells. Now the best boot models all have stiff shells, especially after skiing, and getting out the old fashioned way can cut and badly bruise your instep skin and bones.

Many times skiers get stuck, painfully, half-way-in and half-way-out when they try and take their foot out of the liner and the boot at the same time. Pulling the feet out of the liners and the shell deforms the lining materials and shortens their lifespan.


Best practice is to reheat your SKI BOOT SHELLS to start each season, because at the beginning of each season, after a summer of soft shoes, your feet are not used to ski boots. They have the early season blues. By heating the shells again and inserting the liners to wear around, or better still just arranging to start the first day in HOT-shells, you will automatically avert much of the pain that comes with the early season black and blues. You will be set for the rest of the season.

More Tips in FAQ