A century of change in the footwear industry
Reflecting on how the global footwear industry has changed in many significant ways over the past hundred years.
The design and production of comfortable, long-lasting and well-made footwear has been the goal of shoemakers around the world for thousands of years. As with so many other industries that have played a vital role in civilisation, little changed in the way shoes and boots were made until the coming of the industrial revolution towards the end of the 19th century. However, the real innovations in materials and processes used in the manufacture of footwear have arrived since SATRA was founded a little over a century ago.
Although today footwear is produced using many similar methods to those employed those many years ago, obvious technological innovations in machinery, raw materials, production and testing techniques have changed what was to all intents and purposes a cottage industry into a multi-billion-dollar sector. At the same time, recent decades have seen a distinct shift in factory location away from the traditional industrial heartlands of Europe and North America to the new lands of opportunity, primarily in Asia.
During all this time, SATRA has been providing assistance to footwear manufacturers and material suppliers around the world. From its early days in the UK after being founded in 1919, SATRA has expanded to include members in all corners of the globe, establishing itself as the number one international research and technology organisation for the footwear and leather industries.
Since the end of the 1914-1918 war, there have been major changes in shoemaking – some small and others significantly affecting the industry. In this article, we will investigate the developments of five areas: lasts, alternatives to leather, machinery, footwear testing and the location of manufacturing plants.
New technology in last design
Other than the initial design, the first stage in the footwear manufacturing process is the production of the last. In pre-First World War Europe, lasts were often made from cast iron. As the war started to use up significant amounts of metal, wood was increasingly utilised and became the preferred material from 1919. This was often maple, sourced from Canadian forests that in many cases were owned by the last manufacturers themselves. Copy lathes allowed lasts to be produced rapidly following the creation of a correctly-sized model.
There was no significant change in the way lasts were made until the Second World War, when the first commercial plastics started to be manufactured. Following the end of the conflict, brittle thermoplastics were used to make lasts until the early 1960s. At that time, polyethylene was used for the first time, which proved to be a durable and tough material. Later, injection moulding made the process faster, with a roughly-shaped block being turned down to an accurate last. Between 50 per cent and 60 per cent of the material was cut away during this process, but this was reusable.
Today, manufacture of lasts is a fast process. Computerised digitising allows for the scanning of a model last so it can be reproduced accurately on the screen (see the article ‘The value of digital last assessment’). Software can be used to manipulate the last in digital form, altering such elements as the heel height or adding allowance for an insock. Data stored in a program can be used to cut accurate lasts quickly, with modern machinery allowing a number of different sizes to be formed at the same time. In addition, digitised last information can be shared by e-mail between last manufacturers around the world. Last making was once a craft needing the trained skills of a foundry worker and a carpenter. Nowadays, it requires knowledge of programming and CAD-CAM systems.
At the beginning of the 20th century, cast iron lasts were made in a number of sections which were then often fixed together with interlocking pins. This allowed for the last to be taken apart in order to remove it from the partly-finished footwear without causing too much damage. Wooden lasts also were designed to be broken down, with removable ‘scoop blocks’ held in place by screws or brass springs. Today, plastic lasts are normally hinged to allow removal after the shoemaking process, although in Asia lasts are often made of solid polyethylene to speed up the process.
In the early part of the 20th century, a well-made last would stay in use for 25 years and may have remained in an individual shoe being manufactured for three to six months. Because of this, a large quantity of lasts was needed. Today, a typical shoe stays on a last for a maximum of 20-30 minutes, due to the use of a heat-setting process during footwear production, described in the article ‘Heat setting in footwear production’.
The arrival of alternatives to leather
Animal skins have long been used by man as a protective covering. When skins were first tanned to produce leather, this new material combined a level of water resistance with good insulation and wind resistance, water vapour permeability and high absorbency, as well as being flexible enough to be formed and set into the desired shape.
Demand for good-quality leather, along with rumours of a potential shortage, led some companies to explore the possibility of producing an affordable alternative to this traditional material, which could match the properties of leather. After the Second World War, a wide range of synthetic materials derived from the petrochemical industry appeared on the market. Inexpensively made, these had consistent properties. An early attempt to produce a leather-like material involved bonding a textile base to a polymeric coating. One of the first of these was polyvinyl chloride (PVC) polymer-coated fabrics (PVCCFs), which gave an imitation of the flesh and grain of leather. Such early materials had good abrasion resistance, but low water vapour permeability, poor flex crack resistance and were cold to the touch.
Polyurethane-coated fabrics (PUCFs) were developed in the 1960s and were an improvement on PVCCF. Originally, the materials were made by casting a polyurethane film which was then stuck to the fabric base with an adhesive tie coat. These materials had more of the feel and appearance of leather, and also had a degree of water vapour permeability.
Further advances were made by using a brushed fabric as the substrate to give improved appearance and handle. One of these developments was ‘coagulated PUCF’, in which an organic solvent solution of PU was applied to a brushed fabric. It was then immersed in a non-solvent for coagulation, which resulted in the formation of a porous structure. This increased both the flexibility and water vapour permeability, and gave a more leatherlike appearance.
Poromerics (microporous synthetic leather substitutes) were developed in the 1960s and 1970s and were intended to be an improvement over coated fabric. They were defined by SATRA on their introduction as ‘a man-made shoe upper material, which is generally similar in nature and appearance to leather and, in particular, has a comparable water vapour permeability’.
The application of coated fabrics was limited by the properties of the knitted or woven base fabrics. Poromerics used a nonwoven fabric impregnated with polymer (usually PU), thus producing a more leatherlike material. A wide range of poromerics with diverse structures were developed. The nonwoven substrate offered the closest simulation to the fibre structure of leather, but required significant levels of binder. The aim was to increase the degree of interweaving and reduce the need for impregnation.
Later developments included the development of micro denier fibres to produce materials with characteristics much closer to leather. Hydrophilic fibres were also used to enhance comfort by producing more absorbent materials that had permeable but abrasion-resistant topcoats to mimic the grain, as well as new impregnation techniques, hydrophilic PU formulations and water-based systems.
In addition to being selected for the majority of footwear uppers, leather had been the material of choice for solings until it initially encountered serious competition from rubber in the 1930s. At first, soles were cut from natural crepe rubber – a material formed from natural latex tapped from rubber trees – which has low levels of resistance to solvents and oils, but is both durable and flexible.
Quite soon thereafter, units were being made from vulcanised natural rubber compounds formed using heat and pressure. Vulcanised synthetic rubbers such as styrene-butadiene rubber were then developed, as was rubber reinforced with high-styrene resins (resin rubbers) which provided hard, thin sheet solings that were leatherlike in both feel and appearance.
In the 1960s, thermoplastic solings began to be developed. The first of these – PVC and thermoplastic rubber (TR) – allowed sole production with faster and cheaper processes than were required by vulcanised rubber.
PU solings were introduced at the end of the 1960s. Most familiar in reaction-moulded lightweight microcellular form, polyurethane is also used in thermoplastic grades (TPU).
Since the late 1970s, microcellular ethylene vinyl acetate (EVA) in cross-linked form has proved popular as a lightweight soling material. Developments during the last two decades of the 20th century saw the introduction of soft vulcanised rubber (‘latex’ rubber) as an alternative to TR, and polyolefin elastomers (POE) – elastomeric forms of polypropylene mixed with ethylene-propylene rubber.
Developing new machinery
The demands made by innovative designers of modern footwear forced the development of new technology – from the introduction of large automatic footwear-moulding machines to an improvement in the quality and strength of some of the smallest elements of the shoemaking process – such as the needles used in the stitching process and threads which also have more colour resistance than those used in previous years.
There were a number of ingenious and quite sophisticated shoemaking machines invented in the early part of the 20th century. These included various heel building and heel attaching machines, stiffener moulders, sole moulders, finishing machines, buttonhole sewing machines, eyeletters and skivers. To a greater or lesser degree, these processes have remained very similar even into the modern day.
After cement sole attaching systems were introduced in the mid-1920s, various sole and shoe bottom roughing and cementing machines were developed, as well as a wide variety of attaching presses.
Between 1950 and 1960, high-pressure rubber moulding and vulcanising machines, combined with the introduction of the pre-finished sole, as well as Louis heel and sole units, made considerable impact on the footwear industry.
The decade leading up to 1970 saw the introduction of PVC injection moulding systems, which were followed by the polyurethane reaction injection moulding (RIM) process. The arrival of moist heat setting, invented by SATRA (and for which the Technology Centre received the Queen’s Award for Industry in 1969), dramatically reduced the setting time – and hence, the number of lasts required – and is recognised as one of the great landmarks in footwear manufacture.
In the field of upper preparation, the wider use of synthetic materials led to the use of travelling head cutting presses and, in turn, to processes involving high frequency cutting, welding and embossing. In lasting, the introduction of back-part moulding and seat lasting machines accompanied by developments in forepart pulling and lasting machines – both now with built-in hot-melt cement systems – have also done much to alter the look of the modern shoe factory.
In recent years, computerised machines controlling such processes as pattern cutting and decorative stitching are very common around the world. Little had altered in stitching machinery for more than half of the 20th century, and up to the 1970s, operatives used electric clutch-driven machines, which took great skill and experience to achieve the correct speed. Things changed in the 1970s when the first electronic stitching machines were introduced, allowing the operator to vary the stitching speed by using a foot pedal. Further information on the early use of mechanised stitching can be found in ‘The struggle to develop a reliable stitching machine’.
Testing comes of age
Chemical testing of footwear and components plays a vital role in the production of well-made shoes and boots. Perhaps surprisingly, a laboratory from the 1940s would have looked little different from one in the 1960s, with traditional wet chemistry using burettes, flasks and Bunsen burners being the order of the day.
Things started to change in the mid-1960s, with the introduction of the first infrared testing equipment. Many new test methods – previously impractical to perform – were developed during this period, taking advantage of the availability of more sophisticated analysis techniques. At last, polymers could be accurately identified, as could surface contaminants. Such quickly-gained knowledge brought impressive benefits – for example, the improvement of chemical adhesion – and, in the mid-1980s, chemical testing was further revolutionised with the introduction of chromatography. Bigger and better equipment, mainly developed in the pharmaceutical and petrochemical industries, quickly found an application in footwear and leather testing.
One of the noticeable changes in chemical testing today is the ability to detect incredibly minute quantities of certain substances. Thirty years ago, heavy metals could be quantified to 0.01 per cent, whereas today, modern, highly-sensitive equipment can quantify heavy metals in parts per million or sometimes parts per billion. Also, whereas analysis of organic chemicals was previously very rudimentary, now the detection of fungicides, antioxidants, dyestuffs, plasticisers and flame retardants is normal practice – both qualitatively and quantitatively. SATRA’s work in the field of chemical testing (particularly on discolouration in footwear and detection of restricted chemicals) continues to be of great help to our members.
Physical testing of whole footwear and components has also improved beyond recognition in recent years. From its establishment in 1919, SATRA has been identifying and solving testing problems faced by footwear manufacturers. In recent decades, modern technology has superseded simple mechanical testing of many items, providing access to computerised tests and giving exceptionally accurate results.
Sophisticated whole-shoe tests, such as the Advanced Moisture Management Test (AMMT) and PEDATRON sole abrasion test have been developed by SATRA, providing rapid analysis of footwear problems that previously took months of wear trials to establish. SATRA remains at the forefront of test machinery development and continues to introduce new developments into the footwear industry.
Factories on the move
For most of the 20th century, the main footwear-producing companies were located in Europe and the USA. While there was a small proportion of the overall global shoe production coming from Asia, the traditional strongholds of Italy, France, the UK, Spain, the USA and Germany produced the majority of footwear until the early 1970s. Then, India, South Korea and Taiwan opened up to Western-style mass production of high-quality leathergoods, followed soon afterwards by China. In 1974, European manufacturers produced a little over one billion pairs of footwear, which accounted for 18 per cent of the global footwear market. At this time, the USA manufactured 596 million pairs, which equated to 10 per cent of the world’s market. The Indian and Asian companies by then had secured some 33 per cent of all footwear sold around the globe, producing more than one and a quarter billion pairs of footwear.
With a massive proportion of the world’s population offering cheaper labour than was available in Western Europe and the USA, more and more companies relocated their manufacturing plants to Asia, leading to a swift decline in the number of production units remaining in their traditional homelands.
By 2006, the USA could claim less than 1 per cent of the world’s footwear production, with its factories turning out 32 million pairs of shoes and boots. During the three decades leading to 2006, French footwear manufacturers saw their overall production drop from 237 million pairs to 39 million, Germany’s figure declined from 125 million to 25 million pairs, and in the UK, 5 million pairs of shoes and boots were made – down from 173 million in 1974. Italy and Spain have proved to be the most resilient European footwear producers – although these two countries have seen their output reduce, the downturn has not been by the same proportion as seen in their neighbours. Today, the vast majority of the world’s shoes and boots are made in Asia and the Indian sub-continent.
The footwear industry, which for centuries had used traditional methods of manufacture, has clearly taken technology to heart in recent decades, and this has greatly benefited both shoemakers and shoe wearers. Many changes have been evident – in all aspects of design, materials and manufacture – but perhaps the greatest difference is where most of the world’s footwear is now made. Many European and North American companies in shoemaking and ancillary trades have either closed down or moved their plants to Asia. While there has been talk of shoemaking moving back to the West, there has so far been little evidence of this taking place on a large scale.
Despite current tough economic conditions – not least of all because of the COVID-19 pandemic – there are still reports of shoe producers continuing to provide just what customers want and with sales recovering in many areas. That bodes well for the future of footwear.
How can we help?
Please contact SATRA’s footwear team (email@example.com) for assistance with matters relating to footwear design, testing and production.
This article was originally published on page 43 of the December 2020 issue of SATRA Bulletin.