Microscopic Look at Sneakers
Richard Calmes
Tracey Blaszak
Sean Evans
April 10, 2000
Table of Contents
Introduction pages 1-2
Brief History pages 3-4
Outersole pages 5-7
Midsole page 8
Insole page 9-10
Upper Assembly pages 11-12
Marketing and Economics page 13-15
References page 16
Appendix page 17
Figure 1. View of whole sneaker page i
Figure 2. View of sole assembly page ii
Figure 3. View of footbed page iii
Figure4. Bottom view of midsole page iii
Introduction
The word "sneakers" was defined as "shoes with canvas tops and India rubber soles." Now the word sneaker means a lightweight bundle of polymers and plastic, leather and laces (Vanderbilt, 10). In the global economy, sneakers have had the most success and profit margins. In America alone, over 350 million pairs of sneakers were bought last year. That is why so much research goes into improving sneakers all the time. There have been countless improvements in the design of sneakers since the first one was developed in 1870 after Charles Goodyear learned to vulcanize rubber.
Engineers and chemists have been not only improving sneakers in recent years, but also have been developing shoes for all different occasions. There are sneakers for all high intensity sports, outdoor and indoor, casual and walking. When designing a sneaker, researchers have to take in consideration all aspects of what the shoe will be used for. The questions they must ask themselves are: "What type of traction is the wearer going to need?", "How light must the shoe be to improve the athlete’s ability?", "How comfortable must the shoe be?", and "What conditions does the sneaker have to stand up to?" and still consider looks for social reasons. This project will help us realize what goes into making a sneaker.
There are five main components that make up a sneaker. These components all work closely together to ensure the bodies best overall performance. The components include the outersole, midsole, innersole, upper assembly, and finally the fastener mechanism to hold it secure to the foot.
The figures in the appendix show the break down of a sneaker. This will give you a better perspective of a sneaker. Figure 1. Shows the side view of a sneaker and includes a view into the sole of the shoe. Figure 2. Shows the view of the sole assembly. Figure 3. Show the pattern design of the footbed. Figure 4. Shows the bottom view of the midsole.
Brief History
The evolution of the Sneaker started in nineteenth century England. They were used by the aristocrats for lawn sports (Vanderbilt, 10). They were called "gum shoes" because of their consistency of their sole. Later, in 1839, Charles Goodyear patented vulcanization. >From this process, the modern sneaker was made possible. Sneaker’s got their name from cat burglars or "sneak thieves" that used them to rob places because of their quite and soft soles. In 1897, tennis shoes went on sale in Sears for $0.60 a pair. The sneaker industry began to grow. U.S. Rubber, Inc. introduced Keds in 1916, and Converse, founded by Marquis Converse, produced the first "All Star" sneaker in 1917. B.F. Goodrich and A.G. Spaulding were not too far behind in the industry. After WWI, the sneaker industry expanded quickly as more Americans turned to sports and physical health for the next few decades, the market grew quietly. In the 1920’s and 1930’s, companies added different traction styles for different sports and started producing models for boys and girls. In the 1950’s, the American sneaker market had a major "take off ". More and more families began to move to the suburbs where leisure sport participation was on an upward climb and sneakers were the shoes of choice. This was the first time the sneaker was an integral part of youth fashion and cultural movement. In 1962, sneaker sales doubled. Leather shoe companies were intimidated by this sudden boom and began releasing claims that sneakers were bad for children’s feet. The sneaker manufactures fought back and actually proved that they were beneficial to posture and health. Goodrich became a powerhouse in the U.S. industry of the 60’s. However, foreign companies, such as Adidas, began to target the U.S. market. In the 1970’s, Nike started to advertise heavily and began to appeal to young Americans. This trend has carried on and Nike now owns over 40% of the market. Sneakers have become one of the most profitable industries in the world. The design and engineering is almost as competitive as the automobile industry.
Outersole
The Outersole of the sneaker is the component of the shoe that is mostly responsible for traction and bulk. This part is made up of a sequence of pads relative to one another. The outersole is almost always made out of polyurethane. Thermoplastic polyurethanes are easy to process into many fabricated products but however, the high temperatures and stability needed for sneakers makes these easy made polyurethanes inadequate. Their stability and properties of this thermoplastic must be improved. These help in controlling traction and wears. This is done by "crosslinking." Crosslinking chemical reaction resulting in the formation of bonds between previously chemically independent polymer molecules (Zamore, 11). The crosslinking reaction may be facilitated by several methods in sneakers. One method involves the application of a catalyst and heat to a polymer compound. Another method, which is used most frequently in the past few years, involves exposing the newly formed product to electron or gamma radiation to induce crosslinking (Zamore, 11). The product is then converted from a thermoplastic into a type of polyurethane rubber, which is tough and also has enhanced thermal and solvent properties.
Before this radiation process takes place to crosslink the polymers, the outersole must take shape. This shape is given to the outersole by a process called "injection" molding (1). This process involves reacting aliphatic polyisocyanate and polyahl to form a polyurethane rubber that is injected into a dye mold. The polyurethane is then crosslinked by radiation and the finished sole is peeled from the mold with a pattern already molded into the bottom of the outersole.
The purpose of the shoe has a lot to do with the design. These patterns in the bottom are designed for traction purposes. These vary for many different uses.
Sneakers that involve running or walking often have block or zig-zag patterns that go straight across the outersole for straight on traction control. Indoor sports, such as basketball or indoor soccer shoes, have concentric circular designs and are flat to the floor for extra surface area contact with the floor. This enables the athlete to make sharp cuts on hardwood floors. Outdoor sports usually involve having cleats which are tiny spikes protruding from the sole to grip into sod. Also, the soles have different levels of grip or tackiness. This is controlled by crosslinking or the addition of plastisizors. An indoor athletic shoe would have a softer rubber and an outdoor sport would have a harder consistency to it. The softer rubber would have more grip and wear faster where as the outdoor shoe would rely on cleats for traction and would be hard which wears less (McBain, 7).
The " cross trainer" sneaker is a new design that was though up of a few years ago. The cross trainer was designed to help athletes get prepared for competition. This design starts with the outer sole of the sneaker. When the polyurethane is in its liquid form before it is injected into the mold, composites of soft metals, such as graphie, are added to the rubber to increase the weight of the shoe. Because this is heavier than a normal shoe, it helps build up muscles therefore making it easier to perform during competition.
Other additives are used in the design of the outer sole. One of which is plastisizors, which increases the softness of the polymer at a given temperature. This is because the glass transition temperature is lowered. This helps with designing a sneaker that is used for hot or cold conditions. Processing additives can also be found in the soles of a sneaker. Processing additives help with the injection molding process. The sole will come out of the mold easier and time will be cut from the process. Some shoe manufactures use anti-static additives. This helps prevent the sneaker from building up static charge. This static charge can be released when the wearer touches a conductor and give them a shock. Colorants are used for improving the appeal of the sneaker to the consumers. This additive is almost always used even for white sneakers because the polyurethane has a cloudy composition.
Midsole
The midsole of the shoe is designed for comfort and ventilation. The midsole usually works in conjunction with the outersole and insole. This is because of its placement between the two sections of the sneaker. The midsole is formed of a resilient material such as ethyl vinyl acetate (Alviso, 3). This encasement holds a series of tubes, which extend from the rear of the envelope and project through the sides of the shoe. These tubes have control valves. When the valve is open, the midsole acts as a shock absorbing cushion whereby when depressed by the foot of the athlete, air is expelled form the sneaker through the valve. Then, when the pressure from the foot is released, the midsole inhales fresh air as it recovers its normal shape (O’Dwyer, 8). This action also acts as a pneumatic spring, which helps jumping or bouncing. These devices were first found in sneakers such as Nike Air Jordan’s. The air chambers can be found on most sneakers today. They prevent the runner from getting fatigued too fast because it actually recoils the foot forward. The tubes are springy because of the material in which is used. The tubes are silicon, carbon-Kevlar, or trademark composite such as Duralon, Procyon or Stytherm, which are soft and rubbery allowing a springing action (Vanderbilt, 10). Procyon and Duralon are a light weight and inexpensive polyurethane which makes them a great material for midsoles.
Insole
The midsole is not the only part of the shoe that exhibits comfort. The insole of a sneaker is responsible for much of the comfort and is responsible for the biomechanics. The insole provides two layers: a thin inner like layer such as Sorbothane and a stiffening layer made of polyvinylchloride. Sorbothane is a patented high performance, highly visco-elastic polyurethane material with unique liquid solid properties to allow it to simultaneously absorb shock and isolate vibration, giving it a wide range of real world applications (2). The isolators compress some under load, which allows the isolated item to "float," enhancing the isolation. The surface also slightly tacky, helping to hold it in place during installation and while in use. Figure 1. Shows how shock is absorbed when a force is applied to the sneaker insole. The Sorbothane controls the shock much better than the previously used Neoprene or Butyl.
Figure 5. Shock Control Using Sorbothane Duro 50
Biomechanics are introduced into the insole of the shoe. It is designed and constructed to permit and enhance the normal action of the human foot while in stride or even standing. The insole includes a heel and arch mold shaped approximately to the heel and arch of the foot and pads that form to the toes of the foot. This allows a shapely fit for your foot. It acts almost like a perfect encasing for your foot. Also, the thickness of the toe and heel are made the same to ensure that the muscular and skeletal structure of the body is in a natural position. This will allow the walker or runner to experience a foot motion in harmony with muscular construction of the foot. This enhances the normal foot action the normal foot action experienced while walking from heel to toe. The construction of the insole will prevent jarring or twisting of the foot. Energy will be transmitted in a natural way and ease the action of walking or running.
Also, fabrics or chemicals having a low coefficient of friction can be used to line the foot encasement part of the shoe. This also includes the lining of the upper assembly. This can minimize the development of blisters, calluses, and irritation of the skin. These materials used are silicon copolymers. All three parts of the sole work together closely to ensure the best possible performance from an athlete and still have comfort.
Upper Assembly
The upper assembly is composed of a series of leather or vinyl patches stitched together. This is stretched over a heel stiffener and toe puff. These two devices help reinforce the shape of the toe and heel of the sneaker. The upper is then cemented to the sole of the sneaker by a toluene-based solvent to actually melt the two polymers together. These harden and form a strong adhesive. A water-soluble solvent has recently replaced these adhesives because the toluene vapors have been causing harm to factory workers (McBain, 7).
Since it is hard for sweat to escape through vinyl, many sneaker companies are starting to use nylon webbing or even perforations in the vinyl to allow the foot to "breathe." This is especially popular in running shoes due to the great need for ventilation. The shoe must make sure the shoe is comfortable and the shoe must appeal to the customer. The social aspects of the sneaker manufacturing are the most important part of the upper assembly. The upper part usually varies in colors and styles. This is becoming a large priority to the sneaker market. Teenagers are always competing to have the "coolest" shoes. Sometimes this becomes a problem.
Every sneaker needs a fastener mechanism to hold it secure to the foot of the wearer. Sneakers usually have eyelets punched into the vinyl of the upper assembly in which a shoelace is intertwined to pull the two halves of the shoe together. The holes punched into the vinyl could tear the vinyl and ruin the sneaker. Because of this, the holes should be reinforced with a nylon stitch or a metal eyelet. The shoelaces could be made of cloth, leather, or plastic. However, there is a new and preferred elastic shoelace. This shoelace comprises of a plurality of parallel elastic strands having an outer wrapping of woven polymeric fibers (Jackson, 5). These shoelaces have proved to be much more effective. These shoelaces are easier to tie and have fewer tendencies to loosen while wearing the shoe. Also, it gives a snugger fit and is easier to lace because of its cylindrical geometry.
Marketing and Economic Views of Sneakers
Nike owns nearly half of the sneaker market at about 42.1% and Reebok is second at 16.3%. The following chart (Figure 6.) shows what companies share the market.
Figure 6. U.S. Athletic Footwear Market Share
Over 350 million pairs of sneakers were sold in the United States last year. The athletic shoe companies pull in over $11 billion a year in domestic retail sales. The sneaker industry is a highly profitable market. This is due to low cost of production labor. Many of these companies have been coming under fire for using "sweat shops." These are factories in "third world" countries such as Indonesia, Korea, and Malaysia in which workers are paid less than $1.20 a day. The average cost to make a shoe is about $20.00. That includes materials, duties, shipping, labor, and supplier’s operating profit. This is what Nike pays for the sneaker. Nike then has to advertise, distribute, and get their profit. This adds up to about $35.00. The retailer then buys it for that much and after all their cost’s they sell it for roughly $70.00. The following chart (Figure 7.) shows the breakdown of cost (Vanderbilt, 10).
Figure 7. Why a Pair of Nike Pegasus Costs $70.00
Because labor is cheaper in other countries, many companies have been moving production sites out side of the U.S. The trend, as seen in figure 8., shows a steady decline in domestic production.
The marketing is the most important aspect of selling a sneaker. Nike spends over $300 million in advertising a year. This seems like a lot of money until you consider the amount of money they make in retail sales. Nikes sales total about 900 million dollars a year. This proves that it pays to advertise. They are mainly targeting the athletes and high school aged kids. If the shoe says you can do it, then "Just Do It".
References
Appendix
