By Tim Sprinkle

Jun 08, 2021

When it comes to developing gear to be used in the outdoors, no organization on earth is as stringent or demanding as the U.S. military. It has to be. After all, the gear that men and women in uniform rely on in the field has to tick all of the boxes: it must be light, durable, waterproof, and breathable enough to wear comfortably for days.

When leather is needed to make this equipment, it needs to be able to handle all this and more, or it simply won’t make the cut.

It sounds challenging, but navigating a wide range of different industry demands is typical for leather tanneries and producers, according to Lucas Paddock, chair of ASTM International’s committee on leather (D31) and lab supervisor with Chemtan, a manufacturer of waterproof leather products. What works in footwear might not work in automotive seating, textiles, watchbands, or other applications.

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“Across our industry, people have different things that are important to them,” he says. “What the U.S. military needs and what they're looking for compared to a designer working on a leather motorcycle jacket are very different. But realizing what the end unit is going to be ­– and  having universal tests – are important to understanding what the limitations of certain types of leather are and whether or not it will meet that need.”

The committee was founded in 1971 to develop and evaluate standard test methods, specifications, classifications and support the leather industry as a whole, taking into account all of the numerous applications. Now managing 129 active standards, its charge includes the entire production process from the beamhouse (which typically including soaking, liming, degreasing, and other preparation steps) through tanning, treatment, and more. The general process of leather preparation dates back to the ancient world, but technological advances in recent years have steadily improved the process and quality of the end result, calling for new and updated standards. For example, 50 years ago, fats and oils were still being stuffed between the fibers in order to give leather water resistance. But as technology has improved today, producers have techniques that actually make each individual fiber waterproof, so the specifications have changed.

“Certainly, the focus for us is making sure there's a universal language between the footwear producer, the automotive leather producer, the tanner who is making the leather, and everyone else involved so they can test it and know that it meets the specification for each end product. It’s about protecting the consumer at the end of the day.” 

Here are some of the most impactful standards to come out of the committee, just in the last few years: 

1) Standard test method for whole boot breathability (MVTR) (D8041)

Developed in response to the U.S. military’s need for breathable but durable leather boots, this standard outlines a test method that measures moisture vapor permeability of a piece of leather, expressed as its moisture vapor transmission rate (MVTR), which is one aspect of the comfort of the footwear. The test measures the breathability of a boot upper by comparing the difference in temperature and moisture vapor concentration between the interior of the boot and the exterior environment.

2) Standard Test Method for Corrosion Produced by Leather in Contact with Metal (D1611)

Any leather good that's going to be in direct contact with metal, whether it’s a watch band, a belt buckle, or even some gaskets used in engines, can cause metal corrosion from that contact if not properly treated and protected. This standard set out a test method to determine what type of corrosion is going to occur as a result of being in contact with metal and what in the leather is causing it so it can be prevented.

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3) Practice for Accelerated Aging of Leather (D8137)

Just like a paint manufacturer will coat shingles and leave them outside for decades to watch how the elements age them, leather companies are also concerned with how quickly their products will break down under normal use. This is particularly important in the automotive industry, which doesn’t want to see its full-grain leather interiors stretching out over time or becoming brittle and breaking as people repeatedly sit down and get up off of them over years. That’s not to mention the damage that heat and sunlight can do to unprotected leather in a hot car. This practice determines the rate of leather deterioration over time based on a wide range of factors to determine the service life that can be anticipated from a given type of leather.

4) Standard test method for dynamic water resistance of shoe upper leather by the Maeser Water Penetration Tester (D2099) & test method for static water absorption of leather (D6015)

The application or end use of a leather must be carefully considered, as the does the interaction of the article with the environment, specifically water. Given this reality, testing for water absorption has become very important, and this standard outlines a test method that measures the effectiveness of water-resistant treatments of light leathers such as glove and garment leather, which have no finish. It can also be used to measure the water absorption capacity of insole materials, thus providing a gauge for predicting foot comfort or discomfort. 

5) Standard Test Method for Tensile Strength of Leather (D2209)

The tensile strength test outlined in this test method gives a reliable indication of the quality of leather, since improperly lubricated and partially degraded leathers give low values for tensile strength. This plays into the waterproof qualities of a piece of leather as well as the tactile feel and look of it. Is it firm enough for its intended use? Is it soft enough? This standard is often applied concurrently with the test method for elongation of leather (D2211), which measures the elongation or stretch characteristics of leather produced by a tensile load.

“The leather industry has been important worldwide for many years and continues to be,” Paddock says. “It's a byproduct of the meat industry, so as long as people are eating meat, we'd much rather turn those waste products into durable goods as opposed to wasting it.”*

Tim Sprinkle is a freelance writer based in Colorado Springs, Colorado. He has written for Yahoo, The Street, and other websites.

*A special note of thanks goes out to all D31 committee members for their tireless work in managing these and all of the committee's standards.