CONSTRUCTION OF A HIKING SHOE
After explaining some of the main characteristics of hiking shoes in our last post, this time we’ll discuss the anatomy of a hiking shoe. Construction of hiking footwear depends on the components, materials, and technologies used. Knowing more about these will help you become much more familiar with the world of hiking shoes and will help you choose the best fit for your feet.
There are two basic parts to a hiking shoe: the upper, which is flexible and mold around the foot; and the sole, which is more rigid and lies under the foot. The sole is usually made up of several layers. The insole lies under the footbed and is usually quite thin. The midsole lies between the insole and the outsole and may itself consist of several layers of shock-absorbing and stiffening materials. The outsole contacts the ground and has a tread cut into it. The upper and the sole are made separately. When attached, you get a brand new hiking shoe.
A shoe upper is everything above the sole, i.e. the part of the shoe that encloses the foot and keeps the sole attached to the foot. Upper materials need to mold to the shape of the foot.
The most traditional material for hiking shoe uppers, leather has the ability to stretch (with up to 20-30% when steamed to perform stretch over a last) and retain the stretched shape. Additionally, it’s durable, abrasion and puncture-resistant, and breathable. Leather will retain its ability to transmit perspiration vapor when heat builds up within the shoe. It absorbs and disperses moisture quickly and efficiently. It is also flexible and comfortable. The structure of leather provides good tear strength because the fibers aren’t oriented in any fixed direction. Leather consists of three layers - grain (outermost hair side), inner corium central layer, and epidermis. The first two of these are used in hiking footwear production.
In the production of hiking footwear, the most used types of leather are:
- Nubuck (buckskin leather)
- Suede varieties
There are two basic types of leather: top-grain (made from the outer layer of the cow’s hide) and split-grain (made from the inner layer of the cow’s hide). Top-grain leather is tougher and thicker than split-grain leather. Moreover, it holds water-repellent treatment and its shape better. Full-grain leather is the full thickness of the hide. It’s rarely used in hiking footwear because it’s tough and water resistant, but also thick and heavy. So when you see a label “full-grain leather” on a hiking boot, keep in mind that it’s probably top-grain leather. Nubuck is top-grain leather that has been sanded and polished to give it a smooth finish similar to suede. It’s tougher and more water resistant than suede, which is split leather. Nubuck is popular with bootmakers because it shows scuffs and scratches less than smooth leathers do and has a sensuous feel. Rough-out and nubuck leathers are easily distinguished from suede by their thickness and solidity. For example, mountaineering boots may have 3-millimeter leather, while hiking shoes 2-millimeter or less.
The tanning (treatment or preparation that aids the leather in retaining strength, flexibility, and appearance ) and finishing (covers blemishes, protects and improves water resistance) processes give leather its final characteristics.
Many lightweight hiking shoes and boots copy the nylon-suede design of running shoes. This works well for 3-season hiking. It isn’t a good option for snow, though. Uppers are mostly fabric, often nylon mesh in shoes but usually textured nylon in boots, reinforced with leather, suede, or synthetic leather. This design requires many seams, which are vulnerable to abrasion. Moreover, grit and dirt can penetrate nylon much more easily than leather so such membranes do not last as long in synthetic boots as in leather boots.
Fabric-leather hiking footwear is cool in warm weather, it needs little or no breaking in, it’s comfortable, and it dries more quickly than heavier footwear. It’s also used on many of the lightest, most flexible hiking shoes.
Synthetic leather uppers
Synthetic leather uppers have the advantage of being nonabsorbent and quick dry, though they aren’t very breathable. They often come in combination with nylon.
Soft nylon is lightweight, soft and breathable and has been a very popular material for the last 40-50 years. The range of denier used in most sports shoes is from 70D (finest) to 420D (coarsest). Mesh nylon is available in varying degrees of strength and hardness. One of the biggest advantages it has is its breathability. Unfortunately, nylons' excellent breathability is often compromised when they are combined with non-breathable foams or backing materials. Another problem area is the use of full-coverage adhesives to combine these breathable materials. The adhesives create a barrier to the movement of air across the upper. When used in coarser grades, mesh nylon gives added strength and body to the shoe. The usual denier of mesh nylon thread is about 400D.
Plastic is better than leather at providing the rigidity, waterproofness, and warmth activities like mountaineering and skiing require. PVC coated leathers or fabrics that have been formed into a single piece of waterproof upper material without stitching are widely used in mountaineering boots and ski boots. But hiking boots need to be flexible and permeable to moisture so that sweat can escape. Plastic hiking boots are just too hot and sweaty for backpacking.
The inside surfaces of the upper are often lined with special materials to protect the foot and enhance comfort. A function of the lining is to serve as a buffer zone between the shoe and the foot. The lining absorbs perspiration from the inside of the shoe and the feet and helps prevent staining of the upper material. It needs to be breathable and moisture-wicking. Traditionally, leather, cotton, and synthetics were the most common lining materials used in footwear, including hiking footwear. Nowadays, although soft leather lining can still be seen in some hiking boots, man-made synthetics are getting more and more popular. They have several advantages over other lining materials: lighter weight, less absorbency, better durability and moisture wicking, and quicker drying.
Commonly used materials for lining are woven nylon, terry loop, and meshes. Thermal insulation properties are important too. In a cold climate, the lining needs thermal microfibres, which are used as insulation.
Many boots now feature linings made from waterproof-breathable membranes such as Gore-Tex and eVent. How long they stay waterproof varies because the membrane itself is fragile, and if your feet move in your boots, the membranes can wear out very quickly. The first membranes leaked fairly quickly, but newer ones last longer.
Waterproof-breathable membranes have another big disadvantage. Although they let some water vapor out, they are far less breathable than non-waterproof footwear. Thus they are hot and sweaty in warm weather and if you get them wet inside, they will get dry slow.
You can read more about waterproofness and waterproof hiking shoes soon on our blog. There will be a special article dedicated to waterproof hiking shoes.
The insole is the interior liner placed in a shoe that is in contact with the plantar surface of the foot. It’s usually made of fiberboard, stretch nylon, synthetic foam, or even leather laminated to the top of the footbed’s foam core. The insole needs to be flexible, durable, lightweight, antibacterial/anti-microbial, absorbent and to allow the moisture to pass through it. Many shoes are manufactured with a removable insole that can be replaced with an insole designed for a specific purpose such as odor control, moisture control, arch support, cushioning, reducing foot pain, or foot realignment.
Prefabricated insoles are manufactured for odor and moisture control, arch support, and extra-cushioning. They are mass produced and come in a variety of shapes and sizes that can be trimmed to fit a specific shoe size.
Customized insoles begin as a prefabricated insole, but have added extra features based on the specific needs of the individual. Minor biomechanical changes can be made to the foot by adding additional pads or wedges to the insole.
Custom-made insoles are fabricated from a three-dimensional impression of the individual's foot and require a prescription from a physician. Custom-made insoles are individualized for each patient and designed to change the function and biomechanics of the foot.
Materials used in soling
Rubber is the most traditional material for shoe soles because it’s durable and versatile. Rubber can be used in different forms, though it’s used primarily in highly compressed molded form or with a blowing agent in microcellular form (MCR). Natural rubber (NR) has outstanding stretchability and excellent low-temperature properties, as well as superior resistance to slip, puncture and cutting, compared to PVC. It has good resistance to acids, bases, alcohols and diluted water solutions of most chemicals that are water-soluble. However, NR will be harmed by constant exposure to petroleum and oil-based solvents.
Natural and synthetic rubbers are polymeric materials possessing characteristic elastic properties. Additionally, there are elastomers – substances, including mixtures containing natural rubber that have rubber-like qualities.
Styrene-butadiene rubber (SBR) is low in cost and most commonly used among synthetic rubbers. SBR can vary greatly in quality and composition. It’s a mixture of a natural or synthetic rubber base with additives like accelerators, vulcanizing agents, coloring, filler, and softeners. SBR can be any color and quality depending on the composition and purity of ingredients. A gum color or semi-opaque sole usually indicates a higher quality rubber containing purer materials. However, no visual test can determine the quality of rubber soling. Therefore, the durability and traction of a rubber sole can be identified only through a laboratory analysis or a wear test.
Nitrile rubber (NBR) - The copolymerization of butadiene and acrylonitrile produces these elastomers, which have excellent resistance to petroleum oils, gasoline, mineral and vegetable oils.
Neoprene (Chloroprene, CR) rubber - CR is famous for its balance of properties, unique among the synthetic elastomers. Neoprene has better resistance to oils, ozone, oxidation and heat exposure than natural rubber, but does not have natural rubber’s low-temperature flexibility, preventing its use in low-temperature shock or impact applications.
Micro-cellular rubber (MCR)
MCR is a compounded mixture of natural rubber and additives that have a cellular structure and is used mainly for midsoles and wedges. It can also be used for outsole material on certain shoes.
Ethyl-vinyl acetate (EVA)
EVA is a chemical blend of ethylene and vinyl acetate. It’s particularly well-suited as shoe material due to its low cost (compared to natural rubber), light weight, as well as its cushioning effect. Additionally, it’s odorless and glossy. For these reasons, EVA is often used as a shock absorber in hiking shoes.
PU is lightweight, durable, and versatile. It can be used as a midsole and heel wedge component or as an outsole material.
Typically, polyurethanes have a two-component system. Dual-density PU is a combination of a lightweight midsole and wedge with harder outsole material. These elastomeric polymers are waterproof, UV-resistant, glossy, tough at low temperatures, resistant to stress-cracks and are hot-melt adhesive. They are more durable, but also heavier, more expensive, and aren’t as good shock absorbers as EVA.
Among many thermoplastic materials, PVC is the most widely used, low-cost material for solid as well as expanded soles. Modifiers such as Elvaloy add rubber-like performance to PVC. Typically, PVC is compounded with thermoplastic polyurethanes (TPU) and additional components to become more flexible, abrasion-resistant, oil and water-repellent. PVC has good protection against animal fats, many acids, alcohols, alkalis, bases, oils and petroleum hydrocarbons.
Liquid polyurethane systems
They’re used for producing lightweight soles with good mechanical properties, water, and oil resistance.
Nylon is a polyester resin with a higher melting point that can be used to form a harder outsole when injected. Common hardness grades include Nylon 6, 11, and 12 (from the hardest to the softest respectively).
Source: Hiking and Climbing Boots
This is the location found between the outer sole and the upper of the hiking shoe. Soft, cushioning EVA midsoles in lightweight hiking footwear and heavier but much hardwearing PU are the most-used materials for midsoles. The shock absorption property of hiking shoes, the so-called „cushioning“ is among the most important characteristics of hiking footwear.
The boot sole must support the foot, protect it from shock, and be flexible enough to allow a natural gait. Generally, flexibility is a more important characteristic of hiking shoes than stiffness. The traditional sole stiffener is a half- or three-quarter- length steel shank, only half an inch or so wide, placed forward from the heel to give solidity to the rear of the foot as well as lateral stability and support to the arch while allowing the front of the foot to flex when walking. Full-length shanks are for rigid mountaineering boots, not for walking. Some boots combine a steel shank with a graded nylon insole.
This is the bottom of the hiking shoe that interfaces with the ground. The outsole, with correct traction, gives durability and slip resistance. There are a variety of different materials that are used for outsoles depending upon the activity for which the shoe is designed. Functional properties of the sole are durability, waterproofness, stability, flexibility, rigidity, breathability, thickness, and good traction to the ground.
Аny pattern of studs, bars, or other shapes seems to grip well on most terrain. The key is a pattern that doesn’t allow the shoe to slip. Note that no rubber sole will grip on hard snow or ice. That’s why alpinists use crampons to securely travel on snow and ice.
Generally, the more surface area in contact with the ground the more support the shoe offers the foot.
Some hiking footwear uses the „sticky rubber“. Soles with this material are ideal for scrambling and difficult rocky terrain, but the sticky, soft rubber that grips well on hard, fairly smooth surfaces don’t perform so well on soft/muddy ground. Additionally, it isn’t very durable. Harder rubbers are used for most hiking boot outsoles. They’re more durable and grip better on a wet and muddy terrain.
Many soles combine grip and traction with cushioning. They’re made from a dual-density rubber, as the upper layer is soft and shock-absorbing while the outer layer is hard and durable.
It’s hard to predict tread life but, in general, heavier outsoles with deeper treads outlast lighter soles. The terrain is crucial for wear - pavement and rocks wear out soles faster. Soft ground wears out soles much slower.
A functional fastening system is an important factor in good hiking shoe fitting. The length, width and the place of the fastening maximize or minimize the performance and comfort. Shoelaces are most often either braided or woven from cotton, nylon or polyester. Laces for hiking shoes are usually braided from durable nylon. Round laces seem to last a bit longer than flat ones.
Boots may be laced up using D-rings, hooks, eyelets, webbing, miniature pulleys, and tiny metal tunnels. The easiest system to use combines two or three rows of D-rings at the bottom of the laces with several rows of hooks or speed lacing at the top. Boots with D-rings alone are harder to tighten precisely. Whatever the type of lacing, many hiking boots have a locking hook offset at the ankle that holds the lace in place even when it’s undone.
Heel counters are stiff pieces of synthetic (or leather) material built into the rear of hiking shoes or boots to hold the heels in place and support the ankles. If a hiking shoe is to retain its shape, it is necessary to stiffen it at the toe and heel; this leads to the addition of heel counters. Some shoes have a substantial heel counter in order to provide motion control and some leave this out completely. You usually can’t see them but you can feel them under the leather of the heel.
The materials for the heel counters need to be strong and rigid. Natural rubber latex, EVA, hot-melt adhesive and various biocides are some of the most used materials for heel counters.
Most of the synthetic components chosen as a raw material should show good water and oil repellency and must be able to be tailored well to provide other required functional properties such as strength, toughness, flexibility, and durability, etc.
This is the width of the toe region, although toe box can also include the depth or height of the toe region. Depending upon the toe shape of the individual will determine what should fit the best. If toes are contracted or overlap each other then a deeper toe box is needed.
Toe boxes are usually made from materials similar to those used for heel counters.
Gusseted tongues with light padding inside are the most comfortable and water resistant. Their main role is to keep pebbles, sand, and debris out of your shoe. A disadvantage of gusseted tongues is that if you are not wearing gaiters, snow can collect in the gussets and soak into the boots. On high-ankle and stiff leather boots, the tongue may be hinged so it flexes easily.
One particular problem area for breathability has been the tongue. Because of the need for padding from lace pressure over the instep, shoemakers have long used a thick layer of foam inside the tongue to protect the foot. Because the instep is also an area where blood vessels come close to the surface of the skin, the tongue should also be especially breathable.
Conventional wisdom says the fewer seams, the better because seams may admit water and can abrade. Thus, the most durable and water resistant hiking boots are usually made of one-piece leather with seams only at the heel and around the tongue.
Shoes are in constant contact with the foot, and adhesives are a key factor in keeping the bond between the hiking shoe lining and insole intact during walking. Adhesives’ polymer properties (like inherent water repellency, bendability, rigidity, elasticity and stain resistance) under the conditions of a broader range of temperature and higher moisture retention levels play key roles in ensuring better performance and comfort. Manufacturers’ use of adhesives which result in shoe allergies can be a major drawback for wearers with sensitive skin. The main adhesives used for gluing in shoe manufacturing are urethane, hot-melt, neoprene and natural rubber.
The materials and components of a hiking shoe increasingly meet the performance requirements, with more functional characteristics.
Materials and components have properties which ensure comfort, fit, protection, stability and support. They can maximize prolonged wear and retention of the shoe shape, and also play a role in transferring heat and moisture from the foot. A variety of materials such as textiles, leathers, advanced polymeric materials, and composites are used for making hiking shoes.Materials that can be used for shoe uppers are leather, nylon or polyurethane/neoprene as a solid foam. The main material used for manufacturing outsoles is rubber. Rubber soles grip well on a wide range of surfaces except for snow and ice. Different types of rubber can be used in the hiking footwear industry – from natural rubbers to synthetic blends. Shock absorption is the main function of the midsole. Main midsole materials are EVA (used in lightweight hiking shoes) and heavier but more hardwearing PU. The insole is usually made of stretch nylon, synthetic foam and other materials. It needs to be flexible, durable, lightweight, and to ensure better odor and moisture control. Synthetics are mainly used for hiking shoes’ linings. They are more durable, lighter, wick more moisture and dry quicker than other lining materials. Some other important components of a hiking shoe are a fastening system, tongue, toe box and heel counter.