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Ski Boot Flex - How to Choose Yours (Chart Inside!)

Ski boot flex is a metric that determines the stiffness of your ski boot. You want a ski boot with enough stiffness to support your weight, but enough flexibility to adjust your body position as you ski.

Choosing the wrong ski boot flex can create blisters, toe bruises, shin pain and a host of uncomfortable sensations for your feet.

In this guide, I’ll break down ski boot flex so you know what it means and how to choose the right flex when buying new ski boots. I also include a handy ski boot flex chart to reference.

What is Ski Boot Flex?

Ski boot flex is an important consideration if you’re trying to buy or rent a pair of ski boots. Like with any footwear, you first need to find a ski boot that fits in terms of length, width and style). Once you've figured out your optimal ski boot size, you also need to consider boot flex— that is, how much a ski boot can flex (bend) forward.

Ski boot construction is fairly simple. Your boot is made from a hardened piece of plastic that clips to the bindings on your skis. The hardened plastic is designed to supply resistance to forward movement so you can maintain an athletic stance without feeling like you're going to fall out of your bindings.

Generally, an ideal body position while skiing is one where your body mass is somewhere between centered over your skies and leaning slightly forward. When you lean forward, pressure is exerted between your shins and the front of your boot.

A softer flex rating will allow you to lean forward more and feel the boot accommodate that push. A stiffer flex rating means you can push all you want, but that boot will stay locked in position.

Why is the Ideal Skier Stance Slightly Forward?

A forward skiing position, with a slight bend in the hips and a more acute bend in the ankles and knees, allows skiers to respond rapidly to changing conditions. If you maintain a good, forward body position, you’ll be able to quickly react to sudden terrain changes, moguls, trees, and other obstacles you encounter while skiing. An athletic stance gives you the most control and power.

Skiers who lean back put a lot more pressure on their knees. Not surprisingly, one of the more common injuries in skiing is an ACL or MCL tear from incorrect skiing positions over time. Leaning back also leaves you out of balance over your skis and more likely to tumble if you hit an unexpected bump or catch an edge.

Why does Flex Matter?

Flex matters for your confidence, skill level and general comfort. The ideal flex rating allows you to find your best form and practice critical skiing techniques without being in pain. Improper flex can cause bruising and blisters and turn off potential skiers to a wonderful sport.

In general, a softer flex rating is better for beginner skiers. Learning new muscle movements, handling fear, and dealing with heavy equipment requires a boot that’s a bit more forgiving. A softer boot flex means you can play around with foot rotation, pressure, and form. Softer flex boots are also more comfortable, which makes them great for learning

Above: Rossignol AllTrack Pro 80 W Soft Flex Boot

If you are an advanced or expert skier, a stiffer flex is better. Stiff boots lock in your stance, allowing you to press forward into your boots while executing turns. If you have a soft boot that moves with a bit of pressure, you’re more likely to feel off balance and you risk straining muscles while trying to maintain your form.

Above: Atomic HAWX Prime 120 S Hard Flex Boot

Stiffer flex ratings also help you transfer energy from one ski to the other, which is critical for many advanced skills. Expert skiing is all about small movements yielding big results. If your boot isn’t stiff enough, it won’t respond to these small movements, and you’ll have to commit more muscle strain to link turns.

How to Choose the Right Flex?

Ski boot flexibility is based on a numeric system that's roughly tied to skiing ability. Frustratingly, there is no standard among ski boot manufacturers, so one number may mean two different things depending on who makes the boots.

Still, the differences are small enough that general assumptions can be made. Here are some guidelines you can follow.

Soft Flex (50-80 Women, 60-90 Men)

This is the softest category of flex ratings, and boots in this range are designed to alleviate discomfort for beginner skiers.

Soft flex ratings make it easier to play with body position and work on completing turns. Soft flex boots are also easier to put on and take off. This is a great flex category for leisure skiers who want to be comfortable and aren’t skiing on steep slopes.

Medium Flex (80-110 Women, 90-110 Men)

This is a great flex range for beginner-intermediate skiers. In this flex range, you’ll be able to ski with a consistent body position and begin playing with speed while experiencing noticeable resistance from your boot.

This flex range is also suitable for freestyle skiers. Freestyle skiers are often grinding rails and boxes or flying off jumps rather than taking on steep slopes. A stiff boot would make landing a lot more uncomfortable, so they generally want a supportive boot that is still soft enough to land on.

Stiff Flex (110-130 Women, 110-130 Men)

This flex category is for advanced skiers who generally prefer aggressive skiing. Here, the flex is stiff enough to hold you in place while you work on advanced skills like carving, slalom turns, pivot slips, and speed control on very steep runs. When skiing with stiff flex boots, your legs should be strong enough to handle the pressure of the boot’s resistance.

Very Stiff Flex (130+ Women, 140+ Men)

This flex category is usually reserved for professional ski racing athletes, competitive skiers, and top recreational skiers. Most of the boots in this flex range are racing-specific boots or heavy-duty alpine boots.

Is the Flex Rating Listed on My Boots?

It sure is. Most boots have flex indication numbers written on the outside of the boot cuff. Here, it's visible to potential customers and can be easily referenced when taking your gear into the shop for maintenance or upgrades.

Can the Flex of a Boot be Changed?

Yes. Many ski boots allow for a range of adjustments. These adjustment options allow you to “grow” with your pair of boots as your skiing ability improves.

Some boots will have two screws in the spine of the boot that you can adjust. Other boots may have an adjustment via a cam or plate that can be turned or altered. If you’re not sure, the best thing to do is look up the specifications and features of your boot before messing with it.

Summary

Ski boots are built differently than regular footwear, and one of the biggest differences is that they flex. A softer flex is great for beginner skiers who need comfort and flexibility as they learn to ski. Softer flex boots are also great for terrain park skiers who need softer landings for airborne tricks.

Stiff flex is fantastic for advanced and aggressive skiers. With a stiffer boot, you can maintain a forward body position and stay in control on steep slopes.

I’m happiest on long backpacking trips into little-known pockets of wilderness, skiing down backcountry mountains, and on all-fours, scrambling the rocky spines of alpine ridges. When I'm not adventuring in the outdoors, I'm most likely writing about them.

*The information on this site is based on research and first-hand experience but should not be treated as medical advice. Before beginning any new activity, we recommend consulting with a physician, nutritionist or other relevant professional healthcare provider.