ID Chair and ACX: Customisation and Intuition

One chair was built for maximum personalisation. The other adapts automatically to changing conditions. Antonio Citterio tells us about ID Chair and ACX – two of his most remarkable chair designs. The ID Chair is Vitra’s bestselling office chair. First launched in 2010, it marked a decisive shift in office seating. Rather than a single product, it is a highly flexible system that Citterio describes as “a universe of identities”.

Anniina Koivu: From the outset, the ID Chair was conceived as a modular composition allowing endless configurations. Continuously refined over the years, it remains grounded in its original concept to this day.
Antonio Citterio: We started by saying: “We don’t design one chair, we design a concept for many chairs.” And that’s what ID is – more than a single piece of seating. It is a system capable of numerous modifications, adapting to personal needs. We were aware that design is in constant evolution – as are the offices and individuals for whom the chair is made. So we had to make sure that ID would endure over time.

Your strategy of creating a modular system has turned ID into Vitra’s most successful office chair. Recent developments include aesthetic updates – a broadened colour palette for the chair’s Volo textile – as well as functional additions, such as the optional AutoMotion mechanism.
This is both a rational and an industrial way of designing – especially because ID was always intended for large-scale production. The principle is simple: the structure remains, while the parts evolve. Openness is essential, not only for production logic but above all for the client. The chair may still function perfectly, but you might want a different backrest, new armrests or updated upholstery. It is conceived as a system with compatible components that allow for different configurations, so it can be updated rather than replaced.

You are referring to the Vitra Circle for Contract initiative, which extends product lifecycles through refurbishment, maintenance, component replacement and responsible recycling. How did you design the ID Chair to evolve over fifteen to thirty years – or more?
We began with the base: advanced aluminium technology, high-quality recycled plastics and the best available mechanism for ergonomic office seating. The first generation introduced FlowMotion; today the system also includes AutoMotion, which optimises weight distribution and automatic tension adjustment.

Development is fast and never stops. Components improve, materials advance, production becomes more efficient. Technology is progress. But if the structural connections – armrests, backrest, base – remain compatible, individual elements can be replaced. You might change 30% and keep 70%. That makes a big difference. What happens to the old parts? They can be correctly recycled. We must take this seriously.

When I was young, people reused everything. Jackets were bought three sizes too big to last for years. Nothing was wasted. In the following decades, consumption increased dramatically, but now attitudes are changing again. Products can have longer lives – if we design them accordingly.

If ID was conceived as a long-term system built on modularity and evolution, ACX responds to a different kind of shift in the workplace: mobility. Offices today are fluid, shared and less individual. Work moves between desks, meeting rooms and home – often within a single day. Introduced in 2023, ACX addresses this change not with more adjustment options but through reduction. The chair bypasses complexity with an auto-responsive mechanism that adapts intuitively to the user.

ACX is “the” adaptive chair. A chair is no longer necessarily “your” chair, tailored to your individual needs. People sit here, sit there, change desks, move from focused work to meetings. Different users occupy the same chair throughout the day. You don’t want to adjust lumbar support, height or tension every time you sit down. With ACX, the mechanism adapts automatically – whether you are tall, heavy or light. Self-adaptation was the key idea.

You design at multiple scales – from architecture and interiors to products and furniture. How does moving between these different scales shape your thinking?
I design office buildings inside and out, so I observe how people actually work. Today clients talk about plants, natural light, atmosphere. They care more about emotion and relationships, and less about extreme technical performance.

When I started in this business, the office world was divided – traditional law firms with big executive leather chairs on one side, and early tech culture – with ping-pong tables doubling as office desks – on the other. Today these differences are less pronounced. Lawyers and creatives are closer in attitude. As designers, we must understand these lifestyle changes – and ideally anticipate them.

The self-adaptive chair was not requested by a client. It came from our vision – Vitra’s and mine – and from an understanding that our relationship with chairs is changing. It is difficult to ask for something you don’t yet know can exist. If something works well, you barely notice it. But if it is uncomfortable, you notice immediately. Our idea was simple: remove the need to make adjustments. Let the chair respond automatically.

With ACX, technology becomes almost invisible.
Technology must simplify life. If it complicates things, people avoid it. Look at telephones, cars, lamps and even showers – technology must be intuitive and easy to use. We don’t have the time to navigate technical details in objects and pieces of furniture meant to serve us.

Over time, products that were once serviceable and modular have increasingly become sealed, closed systems. In contrast, your chairs deliberately resist this trend: they can be updated, personalised, dismantled into individual parts, repaired, and ultimately recycled.
Exactly. With furniture, we are fortunately still in the mechanical world. Made primarily of recycled aluminium, high-quality polyamide and recycled textiles, ACX is designed for disassembly, repair and material recovery. A chair can last thirty years or more if designed correctly – because it has been thought through for longevity. Both ID and ACX follow this sustainable logic. We should remember: design is complex. It’s not just about recycling. It’s about thinking long-term from the very beginning.


The architect and designer Antonio Citterio, who lives and works in Milan, has collaborated with Vitra since 1988. Together they have produced a series of office chairs and various office systems, as well as products for the Vitra Home Collection. The Citterio Collection is constantly being expanded.