Sole attachment techniques

The manner in which a sole is attached to the upper defines some of its functional properties and its appearance and can affect the fit of the shoe. Six major types of sole attachment techniques are considered (Fig. 24-4).

Fig. 24-4 Six major types of rocker soles.

The Goodyear welt takes its name from the Goodyear sole-stitching machine that was invented in the late 1880s.¹⁷ This technique is distinguished by its prominent use of a welt. A welt is a narrow strip of flat leather that is chain stitched to both the upper and the insole. The outsole then is lock stitched to the welt. Use of this technique yields a strong and structurally sturdy shoe. In order to provide a flat tread surface, the space between the insole and outsole is filled with ground cork or some other lightweight material. Shoes constructed with a Goodyear welt tend be less flexible and not as lightweight as other types. The Goodyear welted shoe lends itself to the attachment of a metal bracing system better than any other type of shoe.

The Littleway and McKay are two different attachment techniques wherein the upper is fastened to the sole via staples and the outsole then is attached with either lock stitches (Littleway) or chain stitches (McKay).¹⁷ This construction leads to the formation of a very flexible shoe, such as a moccasin or deck shoe.

In the stitchdown process, the upper is flanged outward and then stitched directly to the outsole. This is a simple construction technique and is quite cost effective. The stitchdown may or may not utilize a welt or midsole.

With the cement method, the upper is attached to the insole using a strong glue or cement. In a manner similar to that used in the Goodyear welt construction, the space between the insole and the outsole if filled with material. These types of shoes are lightweight and flexible. Many athletic shoes use this type of sole attachment.

Sliplasting is a technique whereby the upper is sewn to an insole made of a similar material. The outsole then is attached through a cementing process. Sliplasted shoes can be quite flexible and provide maximum shock absorption. Many athletic shoes, such as running shoes and court shoes, are constructed using sliplasting.

With injection molding, shoes are manufactured using a heat-sealing process. The outsole is made from a thermoplastic, which liquefies when heated. Using a special machine, the hot liquid plastic is injected into a form and heat sealed to the upper, rapidly hardening and forming an outsole. These types of shoes are fairly inexpensive to make, but they typically are not available in a wide range of sizes and widths and are not easy to modify or attach braces to. For injection-molded and unit bottom cemented soles, most manufacturers do not use a separate bottom for each last width. Typically, two or three different widths of uppers are used per unit bottom width.

Shoe construction materials

Dozens of base materials and literally hundreds of variations of those base materials are used in the manufacture of shoes. In this section, discussion is limited to general categories of materials found in shoes used in conjunction with orthoses and with or as assistive devices.

Lasts

The shape of a shoe is determined entirely by the last upon which it is made. Each differently shaped last produces a differently shaped shoe. The last is a solid, three-dimensional plastic or wooden model. If a shoe is made to be available in multiple true widths, then the manufacturer must use a different last for each size and width combination. The exorbitant cost of manufacturing the large number of lasts necessary to make shoes in multiple widths is a primary deterrent to many popular shoe companies producing shoes that are available in different widths. A last is measured at as many as 10 points, including the heel-to-toe measurement, heel-to-ball measurement, and circumferential measurements at the ball, waist, instep, and heel.¹⁷ Each time one of these measurements increases, the other measurements increase proportionally to create larger lasts. Different style shoes made on different lasts, even shoes made by the same company, fit differently.¹⁷

Sizes and widths

As variable as last shape is from manufacturer to manufacturer, shoe sizing is just as confusing. There is little or no regulation of sizing in the footwear industry.^5,17 The most widely used scale in U.S. shoe manufacturing is the “common” scale, but what value the manufacturers choose as their baseline size is up to the individual manufacturer. To compound matters, the system itself makes little sense and could be considered archaic.

The shoe sizing system currently used by the majority of U.S. shoe manufacturers today is an evolution of a system developed in England in the mid-1300s AD by King Edward II. King Edward declared that three barleycorns, plucked from the center of the ear and laid end to end, would equal 1 inch. He decreed that 39 barleycorns would be equal to the size of the largest man’s foot, or 13 inches, thereby a size 13. Going backward from size 13, each size would equal one barleycorn, or approximately ⅓ inch. A child’s size 0 was equal to the width of a man’s knuckles, or 13 barleycorns (Edward decided that when an infant’s foot was equal to the width of a man’s knuckles, the time was appropriate for the infant to begin wearing shoes). After going up 13 sizes (or barleycorns) the sizes start over. Therefore, a baby’s foot (13 barleycorns) plus all 13 sizes of children’s shoes (13 more barleycorns) plus 13 sizes of men’s shoes (another 13 barleycorns) equals the length of 39 barleycorns, or a men’s size 13.^7,17

Until the Civil War, mass-produced shoes were not available in “lefts” and “rights”; they were straight lasted shoes that could be worn on either foot.⁷ Twenty years later, Edwin Simpson of New York introduced a variation on the scale that, for the first time, included widths and half-sizes.¹⁹

In the American system, a women’s shoe size is the same as a man’s shoe size plus 1½. So in theory, a shoe that is a men’s size 9 should be the same length as a women’s size 10½.

Depending on the manufacturer, as the width of the shoe increases by one width (e.g., from an A to a B), the total interior girth (or the girth of the last) at the ball of the foot increases by to ¼ inch.

Many other sizing system are in use around the world. In most of Europe (except for the United Kingdom), shoes are sized according to the Continental, or Euro, scale. The Euro scale evolved from a French scale called Paris points. One Paris point equals ⅔ cm. The system begins at 0 cm and increases. There are no half sizes. The Euro scale is a unisex metric system whereby each shoe size is ⅔ cm, less than an American full size but more than an American half-size. To review, a US men’s size 9 equals a US women’s size 10½ equals a Euro size 43.¹⁷

Australia, Japan, Korea, Mexico, Russia, and the United Kingdom all use their own unique systems for sizing shoes.

Off-the-shelf shoes

It is generally accepted that there are seven basic types of shoes; the rest are considered variations of these basic styles.¹⁷ The seven basic shoe types are as follows: (1) boot—any footwear that extends proximal to the ankle; (2) clog—thick, wooden-soled, backless, slip-on shoe; (3) oxford—low-cut shoe fastened with laces; (4) moccasin—oldest form of shoe, low-vamp loafer, originally made entirely of one piece of leather; (5) mule—backless shoe or slipper with low or no heel; (6) sandal—shoe with an upper consisting of an arrangement of straps; and (7) pump—thin-soled, slip-on shoe with varying heel heights.

For orthotics and prosthetics, the two shoe types most frequently used are the boot and the oxford. Shoes that have emerged from the oxford family tree include today’s modern walking, running, athletic and lace-up comfort, dress, and in-depth shoes.