by John Niggl
Have you ever taken a moment to appreciate the advances in technology that have allowed you to walk comfortably on just about any terrain and in just about any condition?
I’m talking, of course, about advances in footwear that have occurred over the past roughly 10,000 years. Today’s stiletto heels and Chuck Tailors bear little resemblance to the first known pair footwear. The first footwear, estimated to be around 7,500 years old, were crude sandals discovered in Fort Rock Cave, Oregon in 1938 (source). As you can guess from the sandals’ age, today’s modern shoes go through much more complex manufacturing processes. And although many of us enjoy the comforts that a well-fitting pair of shoes provides, there are still tests and checks we must perform to be sure that we’re getting a quality pair. True to form, Quality Wars brings you the 10 ESSENTIAL quality assurance tests and checks for footwear. So, before you lace up those boots and head off for your next trek in the Amazon, make sure your footwear is up to the challenge!
Checking footwear dimensions typically involves measuring back height, quarter lateral height, medial quarter height, external toe cap length, and shoe length from heel to toe. Inspectors also measure the lengths of shoes laces, if any, and the dimensions of the shoe box against specifications.
Vulcanized shoes contain polymers that are infused with sulfur to provide more durability, while maintaining the shoes’ elasticity. Basic testing of vulcanized shoes consists of applying tensile stress to the rubber outsole. Many factories that produce this material are outfitted with a testing machine designed to produce data on strength, modulus, elongation, toughness and yield strength based on international standards.
Like toys and many other goods manufactured in a factory, shoes need to be checked for needles and any other metal objects that might be hazardous to the consumer. Testing for needles is generally done by use of a machine that uses magnets to detect metal objects in the product. Such a machine should always be used at the factory that produces the shoes prior to shipment. One needle found in a single shoe of a unit sample is cause for rejecting an entire order.
Footwear should be flexible, and shoe flexibility is particularly a concern for those purchasing running shoes. One should be able to twist, bend or otherwise contort a shoe to a certain extent with relatively little effort and without damaging the shoe. To conduct a flex, or torsion test, grip a shoe from the heel end and toe end and bend the shoe upward into itself, then twist the shoe slightly to simulate torque. Check for any gaps in the bond used to assemble the shoe. Are there any cracks or damage? These are a signs that shoe adhesive strength may be questionable.
Stitch count is an important measure of quality and strength in textiles and, therefore, in many types of shoes that use fabric during their production. Visually count the number of stitches per inch of fabric on a shoe to determine quality. As a general rule, an adult shoe should have at least 8-10 stitches per inch, while a child’s shoe should have 10-12 stitches per inch for added strength.
Certain shoes require more grip for friction than others. That’s why it would be difficult to play basketball with shoes that have a smooth bottom surface. One can perform a simple friction test of footwear by setting a shoe on a flat surface and, without applying any pressure, gently attempting to slide the shoe across. If the shoe easily slides without much resistance, this is a very telling sign of a shoe’s applications and limitations. For more detailed test results, a lab can determine the dynamic coefficient of friction between footwear and flooring under various conditions.
This test, normally used for inspecting high-heeled shoes, can be conducted as simply as tapping the back of the shoe to see if it rocks. Typically, if the shoe rocks more than 2mm in one direction or the other, the shoe is unstable and may be hazardous to the wearer.
Bonding tests are used to determine the ability of an adhesive to maintain its integrity under a certain degree of stress. In the case of footwear, bonding tests can be used to determine adhesive strength between upper and midsole as well as midsole and outsole of a shoe. Special bond test equipment would be needed to measure specific adhesive strengths, which a factory may or may not have.
A rub test consists of checking the color fastness of any fabric by rubbing the outside of the shoe with a dry or wet cloth. Similar to a crocking test used in testing fabrics, a rub test ensures that color will not bleed off from the shoe over time.
Marking tests assess if a shoe is non-marking. One way is to turn the shoe with the sole facing upward and attempt to press a fingernail into the sole. If the sole dents or yields then it is a soft shoe and non-marking. A second test involves rubbing the shoe against or drawing a line with the heel of the shoe on a sheet of white paper with just enough force as not to tear the paper. If a mark is left on the paper, the shoe is not non-marking and fails the test. A shoe that fails marking tests is one that will likely leave scuff marks on hard floors.