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Ski Tips > Gear > Boot Guide

The Recreational Skier's Boot Guide

As Avant Ski expands to cover ski and snowboard gear, starting with boots is a no brainer. Ski boots are expensive, purchases are infrequent, and the buying process can be daunting. Are you wondering where to start with choosing a boot? Do you need a custom fitting? Do you have to trade comfort for performance? Are the extra bells and whistles worth it? We consulted with Nancy Deely, owner of Pro-Fit Ski & Mountain Sports, to develop this guide to the basics about boot sizing, fit and custom features.

Ski boots are the most important piece of gear to own

Your boots are the connection between you and the mountain. Whether just starting out or a seasoned pro, it is essential to have the right boots. If you plan to take at least one trip a year, invest in boots. The one exception is if you are just starting out, it may be easier to rent while developing your skills so you can ultimately purchase a higher performance boot. 

The Anatomy of a Ski Boot
Boot Guide_Ski Boot anatomy


Before heading into the store for your next pair of boots, review our five key considerations.

1. Knowing the right fit. The boot should feel snug, but not excessively so. An overly tight boot can restrict circulation and result in cold feet. Fit determines comfort and performance.

2. Five variables determine fit.


Referred to as “Mondo Sizing.” Think of this as your shoe size metric conversion. The Mondo Point Size simply means the length of your foot measured in centimeters (cm). You can get a sense of your Mondo size using this chart.


Referred to as “Last”, the widest part of your forefoot. This is measured in millimeters (mm) and is relative to the widest point of the reference Mondo Size (25.5 for women’s boots and 26.5 for men’s). Generally, as boots get longer, they also get slightly wider.  Widths impact fit and performance and fall into the following ranges:

Width Fit




Last Width (mm)

95 - 99

100 - 103

104 - 106


Skier Type

Liner Thickness

The third dimension of the foot - its vertical rise or thickness. Many boot models come in Low, Medium and High Volume (designated LV, MV and HV). There is a strong correlation between Volume and Last with higher volume boots having a greater width. However, it is important to check parameters and consider your priorities (comfort, performance, etc). 

More advanced skiers will prefer a tighter boot. A tighter boot provides more control. Looser boots can be more comfortable but are less responsive and may not perform as well.

The liner should be snug around your foot with enough room to wiggle your toes. A good rule of thumb is to take the liner out, and slide your foot  forward so your big toe lightly touches the front of the shell. If you can get 1 to 2 finger widths behind your heel, the boot should be the right size.

3. Flex is critical to performance.

Flex is a measure of how much pressure it takes to bend the boot forward. In general, the more advanced you are, the stiffer the boot you need. Your ability to flex your ankle forward (dorsiflexion) will also be a factor when considering the stiffness of your boot.  An experienced boot fitter will observe your ankle mobility before putting you in the proper boot. To find a master boot fitter near you, go to America’s Best Bootfitters for a location near you.

A higher rating (100-130) indicates a stiffer boot, providing greater support and control over the ski. A lower rating (55-90) is more forgiving and better suited for those starting out or looking to cruise the groomers. Flex varies by manufacturer and is influenced by the type of plastic, design, and/or number of buckles. There is no industry standard, so trying boots on is essential. Remember, boots will become stiffer outside in the cold. The chart below outlines general flex parameters:

Screen Shot 2019-11-18 at 10.47.19

4. Be methodical during the try on process.

Ski boot size and flex calculators can be a good starting point, but there’s no way around a physical fitting. We recommend trying on the 2 to 3 brands that best match your foot type. Take your time, walk around the store, wear the boot for at least 10-15 minutes to get a sense of comfortability. It’s also very helpful to wear the socks that you plan to wear while skiing. Thin is best.  Less is more in a ski boot. You always want to maximize blood flow to your toes!

5. Understanding the Bells & Whistles

Heated Boots

Custom Heat Molding

Cold feet can ruin a day on the slopes. In response, after-market boot heaters in the form of heating elements and rechargeable batteries are available (e.g., Hotronic). Some manufacturers such as Rossignol and Salomon have added Bluetooth compatible heating elements to their boots. Our view is that staying warm is primarily a function of boot and sock fit. But if being cold is a consistent problem for you, and you’ve done everything you can to keep your boots dry and promote circulation, we recommend spending more for this feature. 

Almost every ski boot liner is custom heat moldable, but not every ski boot shell is. If you visit a reputable boot fitter, they will know the difference and have the proper equipment and knowledge to take care of any heat molding services. Heat molding the liner can eliminate the first 2 or 3 day break in period on snow. 


If you have a particularly difficult foot and/or ankle to fit, locate a shop with the Fischer Vacuum System.  This system is the “creme de la creme” of custom boot fitting. It enables the fitter to make the boot bigger where it needs to be bigger and smaller where it needs to be smaller. 

Custom Insoles or Foot Beds

The footbed of the ski boot is like the foundation under your house. If it is not stable, the doors won’t shut properly, the walls will have cracks, and the windows will leak cold air. The same is true of your skiing performance. To provide a stable foundation for your skeleton, your foot needs to be secure from the bottom up. For some, the “stock” footbed is sufficient, especially if you have a flat foot. For most, some arch support and heel support is necessary.


After-market footbeds like Downunders work well. Semi-custom footbeds such as Bootdoc are an excellent upgrade and help stabilize your heel and arch in the ski boot. The ultimate is the full custom heat molded footbed such as Instaprint footbeds by Masterfit.  These will make the ski boot feel like an extension of your body and provide the perfect link between you and the ski.


  • Buying boots that are too big. They may seem more comfortable at the outset, but don’t fall into this trap. Skiing in oversized boots make it difficult, if not impossible to control your skis and then there is nothing that can be done about it. It’s easy to make a boot that’s too small bigger.  It’s impossible to make a boot that’s too big smaller. Make sure to consider the length, width and go for that snug feeling.

  • Buying the wrong flex. Your foot size, height, weight, ankle flex and skier ability are all important considerations.  Find a good boot fitter to help you make the right choice.

  • Buying based on physical appearance. Resist the urge to match your boot color to your skis or outfit. If you must match, start with the boots.


  • Having cold feet. While most are concerned with the fit and performance of a boot, staying warm is a big contributor to overall comfort level. Warmth comes down to having the right sock and boot fit to promote good circulation. You can improve blood flow by loosening your boots and wiggling your toes while waiting for and riding the lifts between runs. Don’t underestimate the value of after-market heaters or heated ski boots.


  • The wrong socks. The right socks are critical to comfort and performance. We like the light or ultra-light Smartwool socks. The lighter sock enables greater circulation in the foot as well as a closer feel for control over the ski. Try this Smartwool sock finder to help determine the best sock for you. Less is more in a ski boot!  Don’t tuck your long underwear into the either!

  • Skiing in wet boots. Equally important, the simplest, but more frequently overlooked, is drying your liners out overnight with a ski boot specific dryer or with a hair dryer. Learn how to take your liners and footbeds out of your shells to expedite the drying process. If you are driving to the slopes, NEVER leave boots in the trunk or in the car overnight.  Your body heat will NEVER heat the boot up.

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