Latest regulations, industry case studies and unbiased articles written by experts
Latest regulations, news and unbiased articles written by experts
The best articles written by experts
The Journal for Employee Protection
  • Latest Issue
  • Trending
  • Press
  • Videos
  • Events

Slip and Sliding Away

Published: 07th Nov 2016


We make much of the role of upper materials in aiding foot protection, but until recently little attention was paid to the role of sole bottoming in aiding that most important function of ambulation, more commonly known as walking.

The basic premise of footwear has a heritage that goes back thousands of years to the basic functional needs of foot protection against hot ground, rough ground or cold weather conditions.

Such lower extremity protection was at first only able to use the local readily available materials and as such we have used a variety of natural materials for shoes, of which leather became one of the most popular choices even as a soling material.

Probably most of our readers are too young to have experienced how uncomfortable the classic nine inch work boots were to wear until they were so called ‘worn in’, a term to denote how a combination of weather and stress conditions on the overall boots would compress the leather fibres so that eventually the leather material moulded to the bony contours of one’s individual foot shape.

There is a reason why the art of shoe repair was so popular during the past century and basic constructions like the Goodyear Welt Construction were so widely used; that was because soldiers and workers alike wanted to hang onto their old worn in boots for as long as they could so they did not have to revisit the painful ‘new shoe’ wearing in process.

Footwear basically for job related activities has long been divided in to two different industries, namely the leather industry and the rubber world of which the use of rubber for soling and then later for complete boots is a relative newcomer by classic leather boot standards.

Rubber is a natural product and first found in the jungles of Brazil by 18th century european explorers.

It was first used and was widely popular as a waterproof coating for basic rugged textiles like

woven canvas. A patent by Charles Macintosh in 1823 gave us the first waterproof overcoat to protect us from the wet and cold weather, a major boon to suffering troops and outdoor workers who already had enough suffering to go through in their daily activities.

The problem was the congealed liquid surface was still sticky and it took a patented process by Charles Goodyear in the USA in 1842 to correct this problem and lay out a manufacturing process that was both simple and effective for mass production, albeit also very time consuming and costly to set up.

Goodyears’ breakthrough was by all accounts an accident after years of costly experimentation. The stabilisation of the material was made possible by the addition of sulphur to the rubber mix and by inserting the material into extremely hot boilers. From this concept emerged the process we now know as Vulcanisation.

The success of the vulcanising process meant that rubber as a footwear soling application became and still is one of the most important soling materials.

At first the rubber soles were masticated in giant mixers with other chemicals and ‘fillers’ and then rolled under pressure as sheeting. From the sheeting, strips and shapes of rubber could be die cut and then hand assembled in what we call the built up process. When these individual hand assembled components were placed in the heated boilers for a controlled period of time, those components moulded into one waterproof piece.

Moulded sports units such as those with traction patterns engraved into their flat surfaces came in the 1920s. The real classic basketball sole patterns we know of today were a product of the 1930s before the second world war and reaching their first zenith of popularity immediately after the same war.

In the world of leather soled industrial footwear, it was again war that brought forth technological change out of necessity.

Mass production

The US Civil War of 1861 to 1865 highlighted the need for mass production of rugged footwear suitable for farming, heavy industry and of course military needs.

As a result of this market opportunity a number of very talented self-trained machinery developers in the New England area of the USA revolutionised how to make shoes using machines.

By 1850 Lymus Blake devised and patented a sturdier version of the then known machines used for sewing clothing fabric, and introduced a lockstitch sewing machine strong enough to sew a leather sole to a leather insole by sewing the join inside the delasted boot by means of an arm device that fed the thread through the needle etc.

Astute businessman Gordon McKay then purchased the patent from Blake, improved the machinery function and renamed the process the McKay stitch. However, it was Charles Goodyear Jnr who really made the greatest change from handwelting to machine welting by again buying a patent from a struggling inventor and then improving the way the machines sewed a leather welt to a ribbed insole in a way that enabled real mass production of leather footwear to take place.

Goodyear filed his patent improvements in 1871 and then tied up a business relationship with McKay and other partners to make such machines for the industry at large. The company they founded was later to become the United Shoe Machinery Corporation and one that dominated the global use of the Goodyear welt Construction because they only leased their machines and never sold them.

The Goodyear Welt Construction revolutionised industrial and classic dress men’s footwear production. Within a decade of its patent introduction, literally hundreds of family shoe manufacturing plants in Europe and across the world were licensing the patent.

By the time Wold War One came on the scene the ordinary soldier was being sent in to battle with basically a one style fits all welted nine inch boot consisting of cheap plated and embossed grain leather uppers and hard rigid veg tanned soles.

Accommodation for terrain conditions then rested with the addition of hob nails, metal cleats, spikes and crampons. For storage of ammunition and fire prevention some forces were required to wear soles that had been attached by wooden pegs to avoid setting off sparks that could lead to explosions.

After the first world war the warriors returned to their civilian life and the Bootmakers had to adjust their offerings accordingly.

Sole evolutions

Vitale Bramante of Varese Italy l is credited with inventing the first non-leather unit sole concept for rugged activities in 1937. He was inspired to do so by a mountaineering tragedy involving some of his friends and an expedition of which he was a part. I personally have read at least two variations of the source of inspiration for the sole bottom design. One uses World War One tank tread patterns and the other refers to bike and car tire track patterns. Logic makes me side with the tire industry as Pirelli, the Italian tire company, was involved in financing the project – Pirelli were rubber moulding specialists and rubber technology was being widely used in industry as plastic technology continued to flounder somewhat.

The Vibram sole became a source of inspiration for many rubber soled products just as the second world war was breaking out.

During the war the concept in the UK was referred to as the Commando tread pattern and was considered the ultimate performance enhancement sole design, helped no doubt by the numerous heroic war efforts of the various marines and special forces who as elite troops were issued such footwear.

This same Commando sole has very much influenced our mindset as to what elements are necessary for a great occupational footwear sole design.

Surfaces like concrete, asphalt, wood, brick, stone, earth, metal, and even AstroTurf are all possible danger zones when we neglect to respect what suitable functional sole tread patterns are needed.

One only has to observe now on a regular basis, how many top level professional athletes are suffering foot and ankle injuries because of ill-conceived choices of footwear to wear for specific conditions.

Coefficient of friction

When it comes to designing effective sole tread patterns I have to admit that when I was a student at the Northampton Technical College’s famed shoemaking course under the direction of the legendary John Thornton, I didn’t spend a lot of time worrying about what the “Coefficient of Friction” was all about.

Later on in my business career, however, I quickly became interested in understanding which materials and tread patterns best suited the different types of surfaces that our shoes had to deal with during their lifetime.

A coefficient of friction, by dictionary definition, is a value we calculate to show the force of friction between two objects.

The coefficient of kinetic friction is the force created between two objects when one of those objects is moving and the other is static. It also can happen when two objects are moving against each other. In simple terms it’s about the power of traction between one surface and another.

How many of you have spent time, even with your young kids for their class science projects, recording how long it has taken a weighted shoe to slip down a specific angled surface and to record those differences that occur in the speed and timing of the drop as a result of surface selection and conditions? Well that’s basically what we do in our technical labs today.

I don’t do a lot of product liability cases, but when they have occurred they have been major ones and they do show the extent to which certain people will go to claim personal injury damages for what they believe were injuries caused by faulty shoe situations. During such trials my experiences of studying what happens to certain materials under certain conditions is important to the rulings that occur.

Industrial footwear is one such area of product liability focus where an accident at work can be more than a sprain, it can be a permanent lifetime injury and in the most extreme of cases can result in death.

Style versus substance

For the past 100 years or more of industrial foot protection, a lot has been done to improve upper materials, upper patterns, insole structures and protective safety covers but we have really paid lip surface to tread design, resting so much of our opinions on how attractive the sole looked rather than really testing the functional qualities of the soling performance.

I am sure by now many of you will be vigorously defending your corporate positions that your products are well tested by your own technicians and independent Safety Standard organisations yet I have to tell you that as more and more products are made offshore I have heard time and again from good shoe people who I respect and trust for their comments that old adage “They just don’t make them like they used to.”

For most of the last century Industrial footwear was designed deliberately to look Robust and Sturdy. It reminded me of my years working in South Africa where some older rural africans buying their dress shoes for exclusive sunday church wear made their decisions based on the weight of the shoes with heaviness being equated with good quality of product.

By the end of World War Two rubber had become available again in greater quantities as our South asian rubber plantations first invested in by forward thinking victorian adventurers, began to be in great demand for industrial applications of which one of the most popular choices was for industrial soling compounds.

The problem with rubber is that it is a naturally heavy material and weight means additional energy exertion for the wearer.

Perhaps the most enlightening design concept involving rubber soling design came from the Vietnam war and was the invention of the self cleaning lug sole specifically designed for the muddy rice paddies of Asia?

The 1960s was the decade of the new plastics. Plastics could be bonded by heat welding and we all recall the successes of the Funk / Doc Martens soling construction, that used the classic Commando sole tread pattern, and was about the only new Industrial footwear construction devised since the pre war direct vulcanized soling process. The trouble with PVC is that it doesn’t perform too well when it comes to tread performance on certain industrial surfaces and appealed much more to a fashion and comfort related audience than it did Industrial and Safety footwear markets.

Then by the 1980s, the rise of branding saw industrial footwear also turn to the use of licensed ‘heavy equipment’ names to market their images.

It became a battle of bold lug patterns rather than a respect for functionality of design. Success was in the image and message you sold rather than what functional benefits the product brought to the occupation.

By the mid 1990s the successes of the performance athletic industry began to influence our industrial designs.

We made midsoles lighter, we encapsulated spongy polyurethane in thin rubber shells and our traction patterns became more athletic herringbone inspired than bold lug treatments.

Much of our mass volume industrial safety footwear became easier to outsource to Asia to make in the same or similar factories as used for athletic shoes.

Then for a brief period of fashion influence, outdoor rugged styling became street popular and the role of intricate technical lug patterns again became de riguer for our industrial footwear coverings.

By the end of the 20th century we saw a great advancement in the development of direct injected compounds and particularly synthetic versions of natural materials like rubber.

This was a period when some manufacturers in Europe in particular decided to fight for their survival using these latest moulding technologies particularly in the arena of moulded boot manufacture.

Developing traction

Today as a result of those efforts and much capital investment we are now learning a great deal about what traction pattern works best under what conditions and with what types of compounds. In this regard Western suppliers lead the world in moulded boot technology.

We have so many differing occupational hazards to face in everyday occupational activities.

The design of our traction patterns must be multi directional and for far too long we have tended to use two directional tread themes rather than build our concepts of lugs and treads from the perspective of functional location needs for job fitted footwear.

Industrial footwear soles do not have to be monotonous in their standard repetition of side wall lug profiling. When we had to lay out detailed blueprints by hand it was a tiresome activity best served by repetition but now with CAD CAM facilities and an ability to render three dimensional shapes quickly by 3D printing, we now have an opportunity to be as exciting with our sole designs as that of any other category of footwear.

Designing true functional soles begins with the compounds to be used as they can have wondrous properties all on their own. Our major western chemical compound corporations are constantly bringing to market new blends with new benefits from a functional point of view.

Today we can obtain compounds that are super light yet durable, we can make surfaces smooth, rough or tacky to surface conditions.

We can now add non slip elements such as fibreglass shreds, finely ground ceramic crystals and sipe like razor thin surface inlays.

New moulding intricacies make it possible to mix and match various compound inlays to the need areas of sole locations.

When it comes to the actual tread pattern designs we have such an opportunity for advancement. Our biomechanical experts have evaluated and shown us what type of lug, suction cup, pivot point and metatarsal flex concepts work best, but where we need more expertise and research is in the role of fast and safe liquid dispersion under foot. We need to get under the walkers to see what happens when soles hit possible slick patches.

Now when designing lug patterns we need to be thinking three dimensionally at all times. We are creating angled shapes for self cleaning performance but now those lugs and layouts also need to be built around liquid dispersal channels that can get much of the causes of slippage to the edge of the product as fast as they can.

The classic side wall lug profile will be still with us for many years but its time now to think about what 3D design and moulding technologies can do better for us and improve our chances of fewer serious employee accidents.

In this regard our challenge is to not just blindly follow what athletic shoes do but to use those Sport related needs as ideas generation for,our own unique safety tread concepts. As an example I submit that the next decade demands that we have the opportunity to concentrate on the designing of less uniform sole side walls.

I see an opportunity for working in features that can include side wall flex-points, roll over channels to help with stability and devise strategically placed side support systems that may very well be removable at times.

Why do I mention the concept of functional removable design elements?

In looking through my research files on the history of lug design in footwear I was made aware again of the time in the mid 1900s when many companies existed that simply supplied moulded replaceable heel parts and adhesive ‘Stick a soles’ for the foreparts of soles. These suppliers had studied the missing needs of consumers and had satisfied that extended durability factor with low cost after sales accessories.

Now, when I take my courier packages from the driver, I’m much more interested in questioning why he is wearing heavy cheap work boots and asking him what features does a job specific courier driving boot or shoe need. I’ve even spent time with roofers working on my house talking about their needs and boy do they have lots of ideas for what they need.


In closing let me proffer that this article, as is my bent, was meant to be a provocative article, I want even CEOs to think a little bit more about function rather than finance. Cost cutting may have short term benefits but if a worker slips because of surface conditions and ill selected product, the costs to the organisation in legal hassles can be enormous.

Share this article with your friends
Phillip Nutt’s family background in work boots, along with Northampton’s reputation for Goodyear Welts and Doc Martens, exposed him to many of the in depth basics of industrial footwear.