Everything you Need to Know about Ski Boot Flex

Published by Harry Sowers on

Why Is Stiffness Such An Important Feature?

Understanding the elements that make up good skiing boots is vital if you wish to safely practice the sport. Stiffness or flex of a ski boot is the term used to indicate the resistance level the boot provides when trying to bend your ankle forward. It’s extremely important to have a good quality boot. Skiing can be dangerous and that’s why having the right equipment is imperative.

How Do You Know If Your Ski Boots Are Too Soft Or Too Stiff?

No industry standard can prove which are the best ski boots. Various variables play a role in deciding whether a particular boot is too soft or too stiff. These include:

  • Weight        
  • Height     
  • Skiing ability    
  • Preferred speed     
  • Your ankles and feet’s bio-mechanics

That’s why the best boots for skiing are entirely dependent on your specifications. What works for one doesn’t necessarily work for the other.

However, particular technology helps in identifying the flex offered by the boot. This is called the flex rating. The flex rating is provided on the side of the specific ski boot. This helps in choosing the correct type of boot for you. A flex index indicates this flex or stiffness. Generally speaking, the flex index is between 50 and 130. 50 being soft and 130 being stiff.

Are your Ski Boots Too Soft?

An easy way to know if your ski boots are too soft is if you experience ankle pains. The biggest reason for boot pain is from rotating or flattening the skier’s foot while placed in the ski boot, and the skis are put on the inner edges.

Boots that are too soft or too big can cause this to happen. The ankle sits too low compared to the boot’s regulated ankle pocket area. This is the result of a ski boot being too soft. Boots that are too soft can also cause your toes to go numb. Boots that have too much space in them can cause cold air to circulate, leading to your toes tightening up.

Another indicator that your boots are too soft is if wearing your ski boots causes you shin pain. Pain in the shins or shin bang is a result of the angle of your tibia (or shin bone) not matching with the angle of your boot’s tongue.

Your ski boots are also too soft if your toes don’t touch the end of the ski boot. There should be little to no heel movement. If the opposite is true, then your ski boots are too soft.

Are your Ski Boots Too Stiff?

Deciding whether a boot is too stiff can be tricky. It should provide a tight fit, as this gives the skier good control. However, this close fit should never cause the skier pain or discomfort.

A common sign that a particular boot is too stiff is if it is causing pain. A boot should have a snug fit, but it shouldn’t be so tight that it cuts off circulation. When wearing your ski boots, you should be able to move your toes. Your ankle and heel should stay stable. If you struggle to move your toes, then odds are it is too stiff.

Pain isn’t the only sign that your ski boots are too stiff. If you are experiencing your toes going numb, then this can be a sign that your ski boots are too stiff. Abnormally stiff ski boots can trap and pinch the nerves in your feet. This leads to your toes, as well as other parts of your feet, feeling numb.

Boots can also be too stiff if you find that you’re leaning backward. If your balance is thrown off or you find yourself in a position that isn’t upright while you’re skiing, your ski boots are possibly too tight. Boots that are too stiff force your center of balance and can be harder to control and turn your skis.

How Much Flex Do I Need In My Ski Boots?

ski boots with stiff flex

Stiff boots are useful for those who are steering and edging. Whereas, soft boots offer the user warmth and comfortability. This makes softer boots perfect for those interested in skiing leisurely on the green and blue runs. Intermediate skiers may look for one that is going to offer them more speed and better turn-carving skills.

The flex needed for each skier depends on what level they are at and what they wish to achieve by using these ski boots. For example, advanced skiers are more likely to go for a very stiff ski boot that provides them with shock absorption. A stiff boot is going to give the advanced skier the ability to perform to their highest potential. Whereas, making use of a softer boot is likely to buckle under the weight and leverage of the skier. This can lead to muscle fatigue due to excessive bending in the knee. 

How To Soften Ski Boot Flex?

Adjustable Ski Boots

Many types of boots are equipped to adjust the flex. An ideal model should be designed with diagrammed instructions showing you how to change the flex. However, this guide mainly involves replacing the rear cuff screws with the supplied clips.

It’s possible to remove the screw by using a three-millimeter key and insert the clip in its place. After this, you need to push the clips in and tap it with a hammer. This should give it a softer flex.

Nonetheless, there may be a more straightforward solution. Depending on the boot, you can screw the rivet in the back with a four-millimeter key to change the flex. All you need to do to reduce the flex is to turn the key to the left.

Breaking The Boots In

Another way of how to soften ski boots is by breaking them in. This is highly recommended for new boots as it softens it and makes it more comfortable on the slopes. Remember that while breaking the boot in, it’s essential to wear only one thin pair of socks when breaking in new ski boots.

Stretching The Ski Boots

Alternatively, stretching your boot can aid in decreasing flex and reduce any pain in the toes. Plastic ones can easily be manipulated by using heat and pressure. It’s possible to stretch the shell in length, but this can only be extended by a millimeter or two.

Loosening The Ski Boots

It’s possible to loosen your ski boots if it’s made from soft materials. These materials are usually found in boots made for intermediate and beginner skiers. We recommend that if it’s made from anything more robust, you seek professional assistance such as a boot fitter.

Along with this, we highly suggest that you only try to loosen your boots if you know exactly what you’re doing. You may run the risk of damaging expensive skiing equipment if you don’t have the knowledge to loosen the boots successfully. Remember that paying to get the boots stretched costs less than having to buy a new pair of boots.

How To Stiffen Ski Boots?

Adjustable Ski Boots

Many different ski boots are equipped to adjust the flex rating easily and stiffen. Ski boot can be adjusted by screwing the rivet on the back of it with a four-millimeter key. To stiffen the boot, you need to turn the rivet to the right.

Use A Ski Boot Insert

An insert is an easy way to increase stiffness. The insert is placed in the boot and gives an overall tighter feel. Some inserts can increase the flex rating from anywhere between 15 and 30 percent. Moreover, the boots’ fit isn’t compromised by using the insert.

Strap Width

Stiffer ski boots tend to have a wider strap width. You can replace your strap to a wider one. This makes the boots tighter as it better supports the upper leg.


A custom boot can help achieve the best flex for that specific skier. The lining and shell play a significant role in determining the flex rating of ski boots. You can change this flex rating and increase the stiffness by adjusting the boots’ shell or the lining of the boots.

The thicker lining is commonly used for beginners and intermediates. In comparison, thinner lining is found in racers’ and expert skiers’ boots. However, many intermediate and advanced skiers manipulate the lining in their boots to fit the flex rating they feel works best for them.

The shell of a skiing boot can be pushed out with a press to adjust the shape to fit the skier’s particular foot best. In doing this, you’re able to obtain a boot forward flex. This is usually done by applying heat to specific areas of the shell. However, the use of new technologies have made this process easier and quicker to get a stiffer boot.

How Can I Make My Ski Boots More Comfortable?

Wearing the correct socks makes a huge difference as it providing tremendous comfort. A good ski sock is one that keeps moisture away from the foot. A synthetic material such as double spun merino wool can ensure that your foot stays dry and warm. To feel like you have the best ski boot, a boot fitter would recommend an aftermarket footbed. This provides better foot support, which ensures better performance and comfort while on the slopes.

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Harry Sowers

Harry grew up outside of Denver Colorado and has been skiing and snowboarding since he was 3. He is most passionate about skiing and when he was in college at UC Boulder he even participated in the olympic trials for the USA Olympic Downhill Ski team.