Additive manufacturing for mass customization: ski boots made to order

Tailored Fits ski boots

Tailored Fits is a small start-up company founded last year in Switzerland to create an industrial solution for mass customization (MC) enabled by additive manufacturing (AM) technology. Its focus is on tailor-made footwear, protection gear and sports gear.

The company’s goal is to integrate the entire value chain of B2B and B2C functions to form a unique digital commerce solution for retail outlets and consumers. To this end, the value chain covers sales, 3D scanning, ordering, automated product design, production and shipment.

The added value of this approach is an accurate anatomical fit of the gear, which supports users’ natural biomechanics while undertaking their preferred sports with a view to minimizing pressure points and pain and reducing fatigue and wear and tear of joints.

To date, one of the most demanding projects that Tailored Fits has undertaken is the development and production of tailor-made ski boots, built around the skier’s feet. The project has been undertaken in a spirit of co-creation in collaboration with Materialise.

Despite the increasing effects of global warming, ski tourism has continued to grow year on year over the last decade in terms of skier days sold per year. Moreover, the average age of skiers is increasing.

The aims of the project included:

  • improved comfort through customized fit;
  • direct power transmission with minimum input from the skier;
  • easy step-in/step-out; and
  • effortless closure system.

The ski-boot market is a competitive one, with an estimated market volume of 3.5 million pairs per year shared between 20 or so different brands, according to a presentation given by Reto Rindlisbacher, chief executive officer (CEO) of Tailored Fits, at the Materialise World Summit (MWS).

Other factors that contribute to a tough market environment for ski boots include the growing alternative rental market and excessive inventory for traditional manufacturing business models, which often results in aggressive discount policies.

For skiers, there are well-known issues associated with wearing ski-boots. They often do not fit well, which in turn often results in pain, and ill-fitting boots often impair performance.

Rindlisbacher identified a number of other issues. Ski boots are traditionally built of a hard, standard plastic shell and a soft liner, and there is a high likelihood that the wearer’s feet will not fit well into the standard plastic shells. The tight closure mechanisms of standard boots also create pressure points that lead to pain and can affect blood circulation, causing muscle cramps. Cold feet are another common result of badly fitting ski boots.

Manufacturers of standard boots continue to attempt to address some of these issues with traditional foot measuring, liner foaming and punching and grinding shells. However, despite the time and money expended, the boots are still causing problems.

Tailored Fits is proposing a different business model that involves 3D scanning, digitally building a tailor-made boot, 3D printing the tailor-made parts and shipping. This approach offers benefits both for retail outlets and the consumer. For retail outlets, it eliminates stock and warehousing issues (and therefore the write-off of unsold goods), while consumers have a personalized product that fits better, increases performance and minimizes discomfort.

Rindlisbacher said the Tailored Fits project involved extensive evaluation of 3D scanning technology. Central to the entire project, it had to be suitable for working in a sports retail environment. It also had to be affordable, easy to learn, fast and small.

Evaluation studies focused on identifying the best way of scanning consumers’ leg and foot position with the correct toe muscle tension, since the quality of the ski boot depends directly on the quality of the metadata generated from the 3D scan. Rindlisbacher explained that before accepting a scan and before starting the liner build, the quality of each scan is carefully verified.

The co-creation angle of the project was the development of the tailor-made inner boot, which involved using 3D printing technology for both prototyping and production. Prototyping was an essential step in the development process, according to Rindlisbacher. It was used to assess different 3D printing processes and identify which most closely met Tailored Fit’s needs.

More than 30 pairs of ski boot liners were 3D printed in thermoplastic elastomer (TPE) and thermoplastic polyurethane (TPU) materials with fused deposition modeling (FDM) and laser sintered materials in TPU. Simultaneously, the company worked on automating the product build in collaboration with Materialise for positioning, leg scaling and toe box build. The development stages also identified finishing options like flocking the inner part of the liner.

Following this first stage, the project progressed with the development of an innovative shell design for the boot, designed around the skier’s foot, with a clean and classy design. The early prototypes were 3D printed with laser sintered polyamide (PA). These were further developed and fine-tuned with vacuum cast shells in rigid polyurethane (RPU).

Designing the tailor-made inner boot involves positioning individual foot scans to produce a tailored boot that corresponds with the wearer’s precise foot shape. This is fairly complex and demands experience to build the toe box by cutting and replacing the forefoot, apply a Boolean difference between the leg and inner boot, define the different shore values of softer or harder segments using different infill structures following the gathered biometric data and finally generate G-code to 3D print the tailor-made liner.

Tailored Fits is 3D printing the tailor-made inner boot using FDM, citing its affordability. The capital machine investment is up to 30 times lower than selective laser sintering (SLS), and the materials have a lower cost per kilogram and lower consumption. Furthermore, the process allows for building hollow honeycomb-type structures that help with insulation.

Rindlisbacher did also mention the disadvantages of FDM, namely the slower print speeds and that support structures are required to provide specific post-processing operations. This highlights that 3D printing process selection always involves a trade-off.

Finishing and assembly in the Tailored Fits process are designed to provide a ‘more classy look and comfortable feel’.

Rindlisbacher was keen to offer an overall process comparison with a traditional ski boot. For the latter, dozens of parts need to be assembled, whereas with the Tailored Fit approach there are much fewer parts and less assembly time. It simply involves ‘putting the inner boot into the outer shell and mounting the closure strap—done!’. The Tailored Fits ski boots are also competitive in terms of costs, according to Rindlisbacher. 

About Rachel Park

Rachel is a passionate advocate of additive manufacturing/3D printing technologies and the industry that has sprung up around it. However, as the hype and hyperbole has gathered momentum, her aim is always to offer a reasoned voice in the midst of inflated expectations and to cut through the noise in order to provide a realistic outlook of how things are.