What’s small, blue, and took nine years to make? For LEGO, the answer is a miniature locomotive-its first-ever mass-produced 3D printed element to appear in a retail set. The debut comes in the LEGO Icons Holiday Express Train (10361), a festive release that quietly signals a major engineering shift inside one of the world’s most iconic toy companies.
The element itself is a miniaturized version of the set’s main steam engine, featuring spinning wheels and a chimney that functions. Injection molding has been the LEGO manufacturing backbone since the late 1940s, but this geometry was simply not achieveable with traditional tooling. Designers Bo Park Kristensen and Jae Won Lee worked closely to exploit the freedom granted by additive manufacturing in producing intricate connectors and internal features molding could not deliver. “October 2025 marks a milestone that has never been done before,” Kristensen said. “We have for many years used 3D prints in our development phase, but it is the first time we use it on a full scale.”
The milestone capped a nine-year development program to develop a high-throughput polymer additive manufacturing platform able to reach consumer-level production volumes. Head of Additive Design and Manufacturing Ronen Hadar framed the accomplishment as LEGO’s equivalent of adopting injection moulding in the 1940s. The team’s aspiration wasn’t to replace moulding but to add to the design toolset – to make 3D printed parts “boringly normal” in future sets.
The production system makes use of EOS polymer powder bed fusion technology in the form of an EOS P 500 platform with Fine Detail Resolution. FDR uses an ultra-fine CO₂ laser that enables highly detailed features in nylon-based materials. The LEGO Group chose the process for its combination of dimensional accuracy, mechanical strength, and surface quality-all vital for parts to mesh properly with billions of bricks already in existence. Already, the company has doubled the speed of output from its machines and is looking for even more efficiency gains. Material selection is central to LEGO’s strict safety and durability standards.
The PA 2200 Nylon 12 powder by EOS features a high reusability factor, combined with a very fine surface finish, while sustainable options like Arkema’s PA11 Rilsan®, processed from castor beans, may be an attractive choice for future consumer-facing products. Lastly, post-processing is of great importance, with technologies developed by DyeMansion making sure color is uniform, with surface sealing that reduces the inherent porosity and susceptibility to dirt of powder bed fusion. From an engineering standpoint, this leap from prototype to mass production required the invention of new workflows. Unlike the decades-honed process control of injection molding, additive manufacturing had to come up with fresh answers for color matching and dimensional consistency, integrating current LEGO quality systems.
The internal mechanisms and fine detailing of the miniature train provided an ideal test case for validating these processes under real-world retail conditions. Historically, LEGO has dabbled in limited-run 3D printed elements-a drafting arm in 2019, a duck in 2022, and a pogo stick in the same year-but these were distributed only to select fans and events. The Holiday Express Train changes that equation, placing an industrially printed part into the hands of thousands of customers worldwide. As Hadar noted, “We can make all kinds of geometries that are not possible with injection molding bricks with internal mechanisms, for example.”
For adult LEGO enthusiasts and additive manufacturing professionals alike, this release is more than a seasonal novelty; it’s a proof point that high-throughput polymer AM can meet the exacting standards of one of the most demanding consumer product ecosystems. While today it’s a single miniature train, the engineering groundwork laid in Billund opens up a path to a future in which 3D printed elements are as ubiquitous-and as taken for granted-as the classic 2×4 brick.
