Leather Ski Boots Construction (Part II)
Source: Heinz Herzog, Backpack Magazine
(Continued from Part I)
Sole Construction/The Lower Boot
You should know and understand materials and construction in order to select a model and brand. Boots are further classified by the manner in which the soles are fastened to the upper boot. The four main methods are: (1) cemented. (2) in-side-stitched, (3) welted construction, and (4) injection-molded. Although the thick lug soles on all boots are fastened with adhesives, the distinctions between the four different methods are quite important.
Boots classified as cemented have the leather of the upper boot folded under a light inner sole, and a one-piece rubber lug sole is then glued on. There is no stitching, no mid-sole, very little support or protection, and the boots cannot be resoled. This is the most inexpensive type of construction and is found only in the trail shoe category. Cemented boots can be recognized by the absence of stitching and the lack of a mid-sole (the mid-sole is the layer of leather or sometimes rubber between the inner sole and the lug sole).
Inside-stitched (or Littleway constructed) boots have the leather of the upper boot turned under and sandwiched between a stout inner sole and mid-sole. The "sandwich" is fastened with a double row of lock stitching concealed within the boot and is thus protected from abrasion. moisture and drying. The soles can be closely cropped (trimmed) so that some hiking boots can double for rock climbing. On inside-stitched boots, both mid-sole and outer sole are easily replaced.
The problems with this simple method of construction are the failure of the sole to flex easily (the inner and mid-sole are stitched tightly together, which stiffens the entire sole) and to mold itself to the bottom of the foot. Soles tend to be stiff, and uppers do not always conform exactly to the shape of the foot. This occurs because the last (the mold around which the boot is formed and made) 'does not remain in the boot until the end of the construction process. Inside-stitched boots require the last to be removed for the stitching operation. Inside stitching is found on many trail shoes, nearly all kletterschues and some hiking and climbing boots. Inside stitching is recognized by the absence of outside (visible) stitching, the presence or a mid-sole and a double row of stitches (usually covered by a synthetic sock liner) in the inner sole.
The oldest and most common type of boot construction involves outside stitching and employs the term "welt." There are several types of welt construction.
The most popular type of boot construction is the Norwegian welt (or storm welt) proven over the years to be both durable and functional. Welted boots are recognized by one, two or sometimes three lines or stitching along the narrow shelf where the upper leather meets the sole. The first line slants inward to securely fasten the leather upper boot to a lip on the bottom of the inner sole. The second runs straight down to fasten the upper, or welt, directly to the mid-sole. The welt itself (which is omitted on a majority of welted boots) is a narrow, somewhat vulnerable strip of leather that runs around the boot on top of the mid-sole and hides the first line of stitching. The third line of stitching is found only on true mountaineering boots.
In a Norwegian welted boot, the cork-filled space between the inner sole and mid-sole permits easier, flexing of the sole, which in turn reduces foot fatigue. The welt also enables the inner sole to conform comfortably and precisely to the shape of the foot because the last remains in the boot until the very end of construction. Norwegian welted construction is the most desirable way of making quality, welted boots and is found in nearly all the climbing and mountaineering models made as well as a majority of hiking boots. Replacing the mid-sole and the lug sole is rather easy, although not as simple as with inside-stitched boots.
Another type of outside-stitched, welted construction is the Goodyear (U.S.) weft. Boots made using Goodyear welt construction have the leather upper boot stitched directly to the inner sole. Then the "welt" or narrow strip of leather is stitched to the mid-sole. The welt and the inseam (see diagrams above) are vulnerable to leaking water and breakage. Goodyear welt construction is not as durable or as functional as the proven Norwegian welt method. Replacing the mid-sole is very difficult. Only the lug sole can be replaced easily.
Injection molding is a relatively new method of making boots. Molten neoprene (a rubber) applied under pressure takes the place of stitching and cement in attaching the leather upper boot to the sole. There are two main types or injection-molded boots. The first type finds the lug sole molded directly to the leather upper boot. This type, found only in trail shoes, is comparable to the inexpensive cemented process. Boots made in this manner are almost impossible to resole. The second type of injection molding uses a separate synthetic mid-sole, usually rubber sandwiched between the molded section and the outer sole, making the boots easily resoleable. This type of injection molding is used mainly for mountaineering boots.
Injection-molded soles adhere well only to boots which use dry (low grease content) leather, which must be silicone impregnated for high water repellency. Injection molding offers economy and light weight, and has some advantages over stitching; for instance, no wear or rotting of the thread, no penetration of water through the needle-holes, and total sole stiffness for technical rock climbing.
The Upper Boot.
The quality of the leather used in construction of the upper boot is also crucial to the fit and performance of the boot. The tanned cowhide used is categorized as either a "split" or as "top grain." When the hide comes off the cow, it is too thick for boot uppers and consequently must be split into sheets of varying thickness. The outside or top layer is called "top grain." It is ideal for boot uppers because of its tough, flexible oiliness and natural resistance to water and moisture. All other layers are called "splits." Though comparatively inexpensive, "split" leather is inferior for boot uppers because it tends to stretch and is difficult to waterproof adequately. A "rough-out" leather may be reversed grain (smooth side in, rough side out) or it may merely be a sueded split, which is not as good. The difference is considerable and important.
The hide of the female animal is grouped by age: calfskin, heifer, cowhide. The hide of the male animal is classified according to its condition. Hides selected for boot construction are divided into two different groups: (I) leather to be used for boot uppers and (2) leather to be used for sole construction (innersole. mid-sole).
The tanning process is somewhat different to achieve the specific features needed for each use. Leather to be used for the upper boot must be flexible enough to fit the last (and foot) exactly but must not stretch; it must be durable and strong to provide support and protection against hard obstacles such as rocks; it also must have the ability to absorb perspiration. Leather to be used for sole construction must have a greater ability to absorb perspiration (and be durable enough to absorb it for a long period of time without breaking down); it should also be lightweight .and have a good bonding ability.
Because seams in the leather upper boot are vulnerable to breakage and water penetration, the general rule is "the fewer the better." This rule applies more to climbing and mountaineering boots, where climbing over rock and ice is commonplace, than it does to trail and hiking boots. Moreover, some people think the two-piece leather upper boot is more desirable for light-duty hiking boots because the two pieces can be formed and contoured to the last precisely well enough to create a low-profile toe on the boot (as opposed to the higher' square-looking box toe used for climbing and mountaineering boots) which makes the boot fit very closely and snugly around the foot from the toe area upward to the front of the ankle.
All boots, except kletterschue and some trail shoes, are lined and reinforced in a variety of ways, using a variety of materials. The better constructed the boot, the better the foot protection and insulation provided. All quality boots should have "heel counters" that cup the heel in a grip that helps anchor your foot to the sole and prevents excessive heel lifting.
Also there should be a stiffened toe. High-quality boots provide "shanks" in the sole to support the arch and protect the instep. The shanks are made of steel, laminated wood or very stiff plastic. Most boots provide foam-rubber padding throughout the ankle area as well as a roll of foam that forms a scree guard or--collar around the top of the boot. The best boots are carefully designed to provide softness and flexibility where possible, limiting stiffeners and reinforcement only to places where they are needed for support and protection. Inexpensive boots often attempt to achieve protection and support by using stiff materials throughout, making the boots heavy, uncomfortable and hard to break in.
The mid-sole above the lug sole (not found in cemented boots) provides stiff-ness, support and comfort. Leather mid-soles help shape the boot to the foot and provide breatheableness and absorption of perspiration which pro-mote a cooler walk. Nevertheless, rubber mid-soles are increasing in popularity with some manufacturers as the price of leather steadily rises.
There is general agreement on outer soles - a lug pattern of high carbon neoprene material is unexcelled. Vibram is the brand currently in vogue, and it is excellent. The softer, lighter, shallower tread of Vibram Roccia (model name) is suitable for trail and hiking boots, but the firmer, deeper, heavier Montagna provides more wear and protection.