Application Spotlight: 3D Printing for Footwear

[Image credit: Adidas]
 
3D printing is shaping new possibilities in footwear engineering, enabling footwear companies to create new shoe designs and address the growing demand for customisation.
 
According to a recent report from a research firm, SmarTech Analysis, footwear 3D printing is set to grow into a $9 billion revenue opportunity over the next 10 years. The firm also suggests that a 3D-printed footwear segment will become the largest 3D-printed consumer product segment by 2030.
 
But what is driving this huge opportunity? 
 
In this week’s Application Spotlight series, we’re diving into 3D printing for footwear, exploring the benefits, use cases and trends shaping the future of the technology in the footwear industry.  
 
Take a look at the other applications covered in this series:
 
3D Printing for Heat Exchangers
 
3D Printing for Bearings
 
3D Printing for Bike Manufacturing
 
3D Printing for Digital Dentistry & Clear Aligner Manufacturing
 
3D Printing for Medical Implants
 
3D-Printed Rockets and the Future of Spacecraft Manufacturing
 
3D Printing for Electronic Components
 
3D Printing in the Rail Industry
 
3D-Printed Eyewear
 
3D Printing for End-Part Production
 
3D printing for Brackets
 
3D Printing for Turbine Parts
 
How 3D Printing Enables Better-Performing Hydraulic Components
 
How 3D Printing Supports Innovation in the Nuclear Power Industry
 

Why are footwear brands adopting 3D printing?  

Currently, footwear 3D printing revenues make up approximately 0.3% of global footwear market revenues, according to SmarTech Analysis. This figure is set to rise to 1.5% of overall global footwear revenues by 2029. 
 
While this growth is encouraging, the actual figure is small when compared to the overall footwear market revenues. This indicates that 3D printing will not replace any of the established manufacturing processes anytime soon. 
 
That said, 3D-printed footwear could become one of the largest segments in consumer products 3D printing. This evolution will primarily be driven by two key trends: 
 
1. The growing consumer demand for personalised products;
2. An increased focus on digital manufacturing.
 

The growing demand for personalised products 

The reality of today’s consumer landscape is that consumers are demanding customised, personalised experiences. 
 
In response, many footwear companies allow customers to order shoes with a limited amount of customisation, for example, by offering a limited selection of colours. 
 
3D printing, on the other hand, allows companies to unlock a new level of customisation thanks to the ability to create shoes specifically tailored to the wearer. 
 
Admittedly, the potential for mass-customised footwear is still in its early stages, and footwear companies are only just beginning to develop strategies to enable shoe customisation en masse.
 
However, as footwear brands become bolder with using 3D printing technologies in production, there will be more options for personalisation.
 

An increased focus on digital manufacturing 

Another key driver for the adoption of footwear 3D printing is the digitisation and automation of production. 
 
Manufacturing shoes is a multi-step, labour-intensive process, and much of the production process is still manual. It requires a lot of specialised machines and workers to manufacture separate pieces and fit them together to create a finished pair of shoes. 
 
With this in mind, footwear companies are looking for new ways to optimise the manufacturing process. 
 
3D printing offers an ideal alternative by enabling footwear companies to streamline the production of certain shoe components. 
 
Unlike traditional manufacturing processes, 3D printing doesn’t require additional tooling to create a part. Instead, the process involves creating a digital model and setting parameters, like printing speed and part orientation, on the build platform, using a specialised software application.
 
The model is then sent to a 3D printer, where another software application automatically guides the printing process according to the digital model and pre-set parameters. This makes 3D printing a purely digital manufacturing technology.  
 
This also means that production can be streamlined while reducing the manual labour involved in the shoemaking process. 
 
All the major footwear brands have been using 3D printing for prototyping and moulding applications for over a decade now. However, recent years have seen 3D printing increasingly adopted to produce functional footwear components. 
 
Producing parts such as midsoles for sneakers has been the most successful footwear application for 3D printing to date. Some brands use the technology to create sneaker midsoles and insoles, while others are experimenting with 3D-printed sneaker uppers and sandals components. 
 

What 3D printing technologies are used for footwear manufacturing?

 
The most common group of 3D printing technologies used in footwear production today is vat photopolymerisation. This group encompasses resin-based technologies like Stereolithography and Digital Light Processing and Carbon’s Digital Light Synthesis (DLS). 
 
These technologies are based on a similar process, whereby a light source (a laser, a projector or light-emitting diodes) is applied to a liquid resin layer by layer, causing it to solidify. 
 
High accuracy, fast printing speeds and compatibility with flexible and springy materials, like TPU, silicone and elastic polyurethane, typical for sports shoes, have made resin-based 3D printing technologies a viable production solution. 
 
In addition to resin-based technologies, shoemakers are also adopting powder-based technologies, like Selective Laser Sintering (SLS) and HP’s Multi Jet Fusion (MJF).
 
These are also optimised to work with elastomeric materials and offer a fast printing speed. However, unlike resin-based technologies typically used for midsoles, SLS and MJF are more commonly used in the production of insoles. 
 

Material developments for 3D-printed footwear

The successful use of 3D printing in footwear production requires production-grade materials, which, until recently, the 3D printing industry has lacked. 
 
Recent advancements in footwear-friendly, 3D printable materials have opened the door for more production applications. This progress has been largely fuelled by close collaboration between technology providers and footwear brands. 
 
For example, Carbon has been working with Adidas to develop an elastomeric polyurethane material used for midsoles in Adidas’ FutureCraft sneakers. 
 
Similarly, New Balance has partnered with Formlabs, a manufacturer of desktop SLA 3D printers, to produce high-performance 3D printing materials suitable for footwear. Together, they have introduced a new proprietary photopolymer resin, Rebound Resin, which is designed to create springy and strong lattice structures. 
 
When printed, the material reportedly displays the same durability and reliability found in injection-moulded thermoplastics. 
 

The benefits of 3D printing in footwear

Faster time to market 

One of the biggest challenges in producing footwear is the cost and time required to create sole unit moulds.
 
Each shoe size requires an individual mould, which can cost thousands of dollars to create. Furthermore, mould manufacturing has long lead times, requiring several months of back and forth communication between the brand and the factories. 
 
In contrast, 3D printing doesn’t require moulds and shoe components can be created directly from a design file, allowing shoemakers to bring new shoes to market much faster.
 
For example, Adidas uses automated shoe manufacturing technologies, including 3D printing, in its Speedfactories in Germany and North America. 3D printing is used to create midsoles for Adidas’ Futurecraft and Alphaedge’s 4D running shoes.
 
The combination of 3D printing, automation and localised production reportedly enables Adidas to introduce the product to market three times faster than with traditional production. 
 

Innovative designs 

 
3D printing enables footwear brands to explore and implement new design features for shoes. Consider midsoles: traditionally, they are made as a solid piece with the same degree of support throughout the shoe. 
 
With 3D printing, shoe performance can be substantially improved, thanks to the ability to create midsoles with lattice structures, which would be impossible to injection mould.
 
These structures can be designed to feature different densities within a midsole. By tuning different areas of a midsole, designers can optimise cushioning properties throughout the shoe, thus creating higher-performing footwear. 
 

Customisation 

 
Another benefit of 3D printing is the ability to create shoes tailored to the wearer’s feet.  
 
To create a custom pair of shoes, companies typically use 3D scanning to capture the individual measurements of a customer’s feet. 
 
Based on the scans, designers generate a design of shoe components, like midsoles or insoles, which meet the customer’s particularities. The design is then sent to a 3D printer for direct manufacturing. 
 
Danish shoe designer, ECCO, is using this approach to expand the personalised experience for its customers. Last year, the shoemaker introduced the QUANT-U footwear customisation project, led by ECCO’s Innovation Lab (ILE). The project takes place at ECCO’s experimental concept store, W-21, in Amsterdam and offers a glimpse into what the future of footwear production might look like. 
 
The W-21 store is harnessing 3D printing in order to provide walk-in customers with bespoke shoes within a matter of hours. 
 
Enabling this is a three-step process which begins from harvesting customer’s data through 3D scanning and wearable sensors. The data includes measurements, like arch contours, foot length, width and volume, toe spacing and body weight distributed across customer soles.  
 
The data is then interpreted and translated into a design of the midsole, tailored to the customer’s feet. The design file is sent to an on-site 3D printer that produces the midsole in a silicone material. Subsequently, the 3D-printed midsoles are integrated into ECCO’s Flexure shoes to offer a perfect fit for a customer.
 
Currently, the QUANT-U project is available only to a select client base. If it proves commercially successful, the level of customisation the project offers could provide brick-and-mortar stores with a competitive advantage in a world dominated by online shopping.
 

Examples of 3D printing in the footwear industry 

3D-printed midsoles 

 
Midsoles — the shock-absorbing layer in between the inner and outer soles — are perhaps the most publicised example of 3D printing in footwear. 
 
For one, sneakers featuring 3D-printed midsoles have been one of the first consumer products to be mass-produced, using additive manufacturing. In 2019, Adidas remains at the forefront of 3D printing in footwear, having reportedly produced over 100,000 pairs of shoes with 3D-printed midsoles. 
 
However, Adidas is not the only company innovating midsole designs with 3D printing. In 2019, New Balance brought a new pair of sneakers to the market featuring a 3D-printed heel component in the midsole. 
 
The 990 Sport runners are the result of a new platform, TripleCell, which leverages Formlabs’ SLA technology and a new proprietary material called Rebound Resin. The resin is meant to replace traditionally moulded ethylene vinyl acetate (EVA) foam. 
 
One of the drivers for this change is the ability to design different levels of support across different parts of the shoe. This is achieved by placing layers of lattice structures with varying densities throughout the heel. 3D printing is the only technology capable of producing such structures. 
 
Through its TripleCell platform, New Balance has developed a new type of springy and resilient heel with the durability and longevity an injection moulded alternative. Importantly, 3D printing also helps the company to localise manufacturing, accelerating the development and production cycles. 
 
Going forward, we expect the development in this space to continue, with more footwear brands jumping on the bandwagon of shoes with 3D-printed midsoles. 
 

3D-printed uppers

 
An upper is a shoe component that covers the toes, the top of the foot, the sides of the foot and the back of the heel. It’s one of the two integral shoe components alongside soles. Uppers are traditionally made of textile, which can be challenging for polymer 3D printers to produce. However, some shoe brands have developed approaches to creating uppers using flexible plastics like TPU.
 
Take Nike Flyprint as an example: this upper is the first 3D-printed textile upper in performance footwear. First unveiled last year, Flyprint uppers are produced with the help of Solid Deposit Modeling (SDM), a process whereby a TPU filament is melted and laid down in thin layers.
 
One advantage Nike’s 3D-printed uppers have over traditionally woven uppers, is greater material durability because the layers are fused together, eliminating frictional resistance common for a knit or woven textile.   
 
If you look closely at the structure of the Flyprint fabric, you’ll notice a few distinct patterns. The front of the shoe features a lattice, while the sides use one that’s a lot more wave-like. Such a design enables the upper to be lighter and more breathable than non-3D-printed Nike’s textiles.
 
Other brands, too, are exploring 3D printing for shoe uppers. For example, independent footwear brand, Oliver Cabell, is 3D printing uppers for its Phoenix sneakers from recycled water bottles. One shoe upper requires about seven water bottles, which need to be first shredded into flakes, melted down and formed into long strands of yarn. These strands are then fed to a 3D printer to create the upper.
 
Uppers remain a less developed application for 3D printing when compared to midsoles. However, it may change over time, as 3D printing could significantly reduce the necessary steps and costs of uppers production. 
 

100% 3D-printed shoes? 

 
While examples of 3D-printed shoe components are abundant, is it possible to 3D print entire shoes? 
 
For now, the short answer is no. However, some companies are coming closer to the vision of fully 3D-printed shoes. Chinese sportswear brand, PEAK Sports Products, is one such company. It introduced a new model of almost fully 3D-printed sneakers in the domestic Chinese market earlier this year. 
 
The upper, midsole and outsole of the new FUTURE FUSION PEAK3D sneakers have been created using a combination of SLS (for the midsole and sole), extrusion 3D printing (the upper) and a TPU material. However, the insole and inner textile are evidently created using traditional methods. 
 
In addition to sneakers, we’ve seen a lot of news around 3D-printed sandals, including Wiivv’s sandals, which was one of the most funded 3D printing campaigns on Kickstarter. 

 
However, 3D-printed sandal is a misnomer, as only some of the sandals’ components are 3D printed. For example, in Wiivv’s sandals only arch supports are apparently 3D printed, while other components are produced using more traditional means.
 
3D printing entire shoes is a fascinating idea, but it currently remains unfeasible. 
 
For one, the technology can’t replace all the processes used in shoe manufacturing while staying economically viable. When compared to traditional manufacturing, 3D printing technologies are slower, less scalable and have significantly higher prices for materials. This makes achieving mass-production with 3D printing a challenging task. 
 
The second issue is associated with the footwear manufacturing value chain. Shoe manufacturing involves the creation of a last, which is a 3-dimensional wooden or plastic mould upon which a shoe is constructed. 
 
Adopting 3D printing for entire shoes would eliminate the need for a last and would require manufacturers to completely rethink the production, impacting suppliers and stakeholders across the existing value chain. The need for a significant step-change is another factor putting 3D-printed shoes out of reach, at least for now. 
 

Creating new opportunities in footwear with 3D printing  

By combining new materials and digital manufacturing, 3D printing is opening the door for innovative footwear products. 
 
Currently, the technology is facilitating the production of high-performance sports shoes and customised sandals through 3D-printed shoe components. This allows footwear brands to expedite time-to-market while exploring new designs and introducing greater customisation options. 
 
Despite these benefits, the use of 3D printing in footwear remains limited, as the technology currently lacks the scalability to accommodate the intensive and high-productivity needs of the shoe industry. 
 
That said, footwear 3D printing will continue to evolve, driven by the trends in digital manufacturing and the demand for personalised experiences. 
 
Of course, adopting 3D printing will create some challenges in the footwear value chain, and addressing them will take time and effort. However, the reward in the form of unique product and service offerings may be well worth it. Ultimately, the footwear industry could become the first major adopter of 3D printing for mass production of consumer products.