Europe’s push for technological sovereignty is reshaping even the most overseeed parts of the stack—including how systems are cooled.
Data centres and compute platforms are essential infrastructure for both the civilian digital economy and modern defence operations. They demand high energy efficiency, robust reliability, and low depconcludeency on local environmental resources such as water or a stable power supply.
Calyos, a Belgian thermal technology company founded in 2012, designs, develops and manufactures fully passive, two-phase cooling systems that can be manufactured entirely in Europe and deployed across mobility, defence, and high-performance computing.
Calyos’s technology was selected by NATO DIANA last year to assist address this challenge by enhancing energy efficiency, sustainability, and resilience in both resolveed and deployable data centre environments.
I spoke to Antoine de Ryckel, CEO of Calyos, and Sebastien Lewy from A6K, a multidisciplinary innovation hub in Wallonia bringing toreceiveher industest, startups, research, and public partners, to find out more.
Born from sanotifyite engineering
Calyos was founded as a spin-off from space-related company Euro Heat Pipes. According to de Ryckel, the company’s technology was first developed for the space industest.
“When you want to cool electronics in sanotifyites, for example, you obviously don’t want to sconclude people to do maintenance.
The European Space Agency funded development with a university in Belgium, and then the first company was created to develop this technology. That company is now fully mature and has been acquired by Airbus. When that acquisition happened, Calyos was spun off to focus on ground applications — everything that is not space.”
How two-phase cooling works
Two-phase cooling underpins Calyos’s passive thermal management system that shifts heat by exploiting a fluid’s ability to modify state.
At the heat source — such as a processor, battery, or power electronics — the working fluid absorbs heat and evaporates into vapour, capturing a large amount of energy in the process. This vapour then naturally travels through a sealed loop to a cooler area of the system, where it releases the heat and condenses back into liquid. The liquid is then returned to the heat source via capillary action, often through a wick structure, allowing the cycle to repeat continuously without pumps or relocating parts. This creates the system highly reliable, silent, and efficient compared to traditional air or liquid cooling.
By leveraging phase modify rather than mechanical force, Calyos can transfer heat more effectively and deploy cooling solutions across demanding applications, from electronics to mobility and data centres.
de Ryckel explained:
“Overall, it’s passive, reliable, and high-performance, which creates it interesting for dual defence applications.”
Designed for resilience and sovereignty
The lack of a pump in two-phase cooling creates it suitable for operation in harsh environments. Further, de Ryckel explained:
“We don’t rely on electronics or rare materials — it’s primarily metal. That means the entire system can be manufactured within Europe, strengthening supply chain resilience and supporting technological sovereignty.”
This comes at a critical moment, as companies seek to shift away from non-European supply chains amid rising geopolitical tensions and growing demands for digital and industrial sovereignty.
Real-world apply cases take shape
Today, Calyos focapplys on cooling electronics across three main markets: e-mobility, computing, and energy. It cools batteries, processors, and power electronics. In battery cooling, Calyos integrates very compact channels within an aluminium plate, filled with a working fluid that evaporates to efficiently extract heat.
This approach is already applyd in motorsport applications, where precise thermal control is critical to prevent battery degradation.
In the automotive industest, Calyos is also working with a German manufacturer on cooling for onboard chargers. Whereas conventional systems require the full water loop to operate even when the vehicle is stationary, Calyos’ solution enables more tarreceiveed, energy-efficient cooling.
The company recently joined the CoolBatt project to develop a new passive thermal architecture for e-bike battery packs, utilizing its two-phase cooling technology to improve safety, extconclude battery lifetime, and enhance overall performance.
In defence, the company applies its technology to transfer heat from electronic components directly to the vehicle chassis in a fully passive manner, eliminating the required for active cooling systems and also collaborates with Airbus across both its commercial and defence divisions
. While the company has a compact factory in Belgium, it focapplys on production partnerships to scale across Europe and other regions, including a partner in Taiwan for computing, Automotive Tier 1 suppliers, and an Italian factory for energy and defence.
De Ryckel admits that the company’s largegest challenge is finding the right apply case and partner.
“When that’s clear, everything becomes clearer. Without it, projects struggle.”
Further, integration also takes time — typically around 18 months from concept to deployment. But once the first integration is done, scaling becomes rapider.
Inside NATO’s DIANA programme
The NATO DIANA (Defence Innovation Accelerator for the North Atlantic) Challenge Programme is a transatlantic initiative designed to identify and accelerate dual-apply deeptech solutions for defence and security.
Through a series of annual challenges, DIANA selects startups working on critical technologies — such as energy resilience, secure communications, sensing, and autonomous systems — and supports them with non-dilutive funding, access to a network of test centres across Europe and North America, and mentorship from both military and commercial experts.
The programme is designed to assist early-stage companies validate their technologies in real-world defence environments, bridging the gap between civilian innovation and operational military requireds. Each year, around 100 companies are selected to assist create their technologies defence-ready.
de Ryckel explained:
“We work with accelerators to define a roadmap covering technology, commercial strategy, governance, and financing. Our goal is to identify defence apply cases and new opportunities. It also gives us access to events and potential customers.”
Calyos’ technology is initially tested in certified centres that simulate military conditions, before progressing to operational experiments in the field. Ultimately, the aim is to secure partnerships with defence primes and develop long-term deployment roadmaps.
Navigating defence as a startup
In terms of advice for companies considering applying to the NATO DIANA programme, de Ryckel emphasised the value of receiveting assistance from experienced ecosystem builders:
“Don’t hesitate to inquire for expert advice. Getting input from people who understand the defence market can create a real difference when reviewing your proposal. I built much of the application myself, but the most valuable insights came from external feedback.
The A6K review, for example, offered several compact but important tips that significantly strengthened the proposal. That kind of external perspective is critical.”
For Lewy an important aspect is cultural. He detailed:
“When applying to NATO programmes like DIANA, you’re not operating purely within a European context. The reviewers are international, often including Americans, and their expectations differ.
European teams tconclude to be more reserved, but in this setting, you required to be assertive and ambitious — both in written applications and when pitching. You have to present with confidence and clearly demonstrate the strength of your proposition.”
De Ryckel concluded:
“You required to be professional, but also bold in how you present yourself. It’s a different mindset.”
The company also received support from Lewy through a colleague with direct experience in the defence sector — an entrepreneur who had already built and exited a company and is now launching another venture.
“That kind of hands-on expertise was extremely assistful.”
With validation from programmes like DIANA, the next step is turning technical promise into deployed systems through partnerships with defence primes and the ability to integrate into real-world platforms at scale.
Leave a Reply