Boot lab: Boots under the microscope
- Author: Martino Colonna
- Photographer: Giovanni Danieli
For the second year we've lab-tested the flex, walk and thermal insulation properties of all unisex boots in the Light, Tour and Free categories. The results confirm much of what we already know and reveal much that is new, not least regarding the issue of sustainability.
Considering the many innovations showcased in the last edition of the Buyer's Guide, for this season we’ve decided not to modify the test procedures carried out by Sport Technology Lab on touring boots: these are the four-angle flex tests, the walkability tests, the thermal properties tests and the analysis of eco-friendly credentials. Only minor improvements have been made to the test setup to increase rigidity and speed of execution.
Flex testing
The flex was measured at four angles (fore and aft, at both 45° and 90°) to provide information across all usage areas of the boot during descents. The protocol, applied forces, buckle closing procedure and temperature are identical to last year. The prosthesis used and friction-free ankle joint are also the same. As we mentioned previously, some minor tweaks have been carried out to the locking and rotation system of the test instrument base to make it more rigid.
For each category, we’ve rationalized the flex data by giving a value of 10 to the boot with the highest stiffness index at 10° of flex (for the forward 45° and 90° flex tests), and 4° for the rear flex test. The complete curves can be viewed in the online version of the Buyer’s Guide. These graphs also allow you to evaluate how progressive, regressive or linear the boot's flex is by inspecting the shape of the curve. All values are reported in the individual product spec sheets.
Walkability testing
The ski/walk mechanism was set to walk mode and the buckles were located on their respective catchplates as per the manufacturers’ recommendations. Velcro straps, where present, were left completely open. The boot was locked rigidly in place as in the flex tests so as to only evaluate the movement between the shell and cuff. We’ve reported the data as a torque value (in Nm) required to reach a 20° forward and backward angle. The complete curves (available in the online version) provide important information on the force required to rotate the cuff as a function of the angle of rotation. In practice, you almost never reach a fore or aft angle of 20° when walking but stop long before this. This means there are boots that rotate very well up to 15° and become more rigid above this. For many tourers, these can perform equally well in walk mode compared to products that have much lower values at 20°. All values are reported in the individual product spec sheets.
Thermal insulation testing
Heat dissipation was measured with a temperature gradient between the inside and outside of the liner of 37°C to simulate usage with an external air temperature is zero degrees. Based on the results of the insulation testing, which is similar to that used for evaluating insulation classes for buildings, we’ve created a linear efficiency scale using a letter rating system, where class A provides the best insulation and class F the worst. The temperature was measured after five minutes and averaged over the fore and aft sections of the liner. To define our class A rating, we used the boot with the best thermal insulation of those tested as our reference, while class F corresponds to the hypothetical sceenario in which the temperature of the liner drops to 35°C (which fortunately never applied to any of the liners tested). All values are reported in the individual product spec sheets.
Sustainability testing
The boots were evaluated based on the following criteria:
- the presence of material from renewable sources (non-biodegradable) in the shell and cuff;
- the presence of recycled material;
- the possibility of disassembly for potential recycling.
Regarding design for recycling principles, we evaluated the possibility of separating the boot into its component parts (shell, cuff, buckles and other hardware) using basic screwdrivers. We gave negative evaluations to the use of rivets for fixing the shell to the cuff and attaching buckles, parts molded using materials with different physical compositions (bi-injections and over-molding), and glued components. The presence of rivets also prevents parts being replaced if they break, making it necessary to replace the entire boot. All values are reported in the individual product spec sheets.
Tour and Free: ever closer
Flex tests showed the stiffest boots were those in the Free class, with an average of 148 Nm at 10°, followed closely by the Tour class, with an average of 143 Nm, and the Light class, with an average of 100 Nm.
Compared to last year's tests, we’re seeing a convergence between the Tour and Free classes, while the Lights are basically unchanged. Note however, that, unlike all the boots in the Light and Tour categories, which always use have polyamide-based materials for both the shell and the cuff, some Free boots have parts in polyolefin (for example the cuff on the Lange XT3 Free and Salomon Shift Pro) or in TPU (the shell on the Lange XT3 Free, Scott Hint, K2 Mindbender 140 and shell and cuff on the K2 Diverge, Atomic Hawk Magna and Prime). These materials are much more sensitive to temperature changes because their rigidity increases as temperature decreases, so it’s conceivable that at 0°C (32°F) they are similarly rigid—or indeed more rigid— than boots constructed entirely from polyamide. The stiffest boots in the Tour category are the Scarpa 4-Quattro XT and La Sportiva Vanguard, followed closely by the K2 Dispatch Pro and Scarpa Maestrale RS. Among the Light models, the stiffest are the Scarpa F1 XT and La Sportiva Skorpius CR II.
In the Free category, we saw a completely different stiffness trend in three boots with a Cabrio design, namely the Scarpa 4-Quattro Pro, K2 Diverge and Dalbello Cabrio. These are stiffer than all the others, especially in the first part of the curve, and then this tends to diminish. This phenomenon can be explained by the fact that the tongue immediately begins to provide strong support compared to the overlap designs of other boots that have a more linear flex. It should be noted, however, that almost all of the overlap boots tested have at least one component between the shell and cuff in TPU or polyolefin with reduced rigidity at the temperature at which the tests were carried out. Plus, there are new, more rigid TPUs on the market whose performance is less influenced by temperature than the traditional TPUs used in alpine race boots. To sum up, since we don’t have information on what type of TPU was used, it’s not possible to make unequivocal statements regarding this aspect. In the 45° and 90° flex tests there are few differences between Free and Tour boots, indicating that, weight for weight, the stiffness of many boots in the Tour category offer very similar performance to those of the Free category.
Tour: better walkability than Free but slightly less stiff
In the walkability tests, however, we saw a clear difference between the boots in the Light class (average 18 Nm forward and 12 Nm backward), the Tour class (24 and 18 Nm) and the Free class (37 and 31).
In practice, Tour boots have much better walkability than the Frees despite having similar stiffness characteristics when skiing. The boots with the best walkability in the Free class are the Dalbello Cabrio for forward flex, and the Scarpa 4-Quattro Pro for rear flex, with values close to those of the Tour category. Here, the clear winner is the Dynafit Ridge Pro, with outstanding results (7 Nm forward flex and 7 Nm rear flex), and even compares favorably to boots in the Light class. The best result in the Light class is the Atomic Backland Ultimate, which is the only boot that comes close to the Dynafit Ridge Pro.
Free: how warm will your feet be?
The results of the thermal tests showed that the liners in heavier boots in the Free category have on average better thermal insulation, with all values rated class A or A/B, while in the Tour class, four boots received a B-rating, eight an A-rating and one an A/B rating. Finally, all boots in the Light class received a B rating except the Dynafit Blacklight which is B/C.
Ever more models use naturally-sourced raw materials
As for environmental sustainability, only the cuff of the Scarpa F1 SE and the liner and strap of the Scott Re-Source are made from recycled materials in parts other than the sole (like for example the Atomic Backland XTD and Salomon MTN). More boots than ever are being made from naturally-sourced materials (14, compared to 9 last season), in particular Pebax RNW and Grilamid Bio (obtained from castor oil) and, for the first time, we’ve seen a TPU obtained from natural sources being used (in the Scarpa SE). It’s essential to underline that the use of naturally-sourced raw materials doesn’t change the material’s mechanical properties and durability, nor does it mean that it’s biodegradable.
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Probably The most accurate ski test out there.
