Design by Antonio Citterio, 2008. By Vitra. With innovative technology that is neither showy nor hidden, the AC 4 Task Chair creates a balance between advanced ergonomic functionality and subtle design. Three-zone comfort includes an integrated lumbar zone, a flexible zone for the upper back that reduces tension and pressure on the discs and straightens up the neck and head, and a supportive shoulder zone which keeps the neck muscles relaxed, making it easier for the user to maintain a horizontal view of the screen. The AC 4 Task Chair features a synchronizing mechanism, with large opening angle and automatic weight adjustment of the backrest resistance, ensuring that the user's weight is supported in every sitting position. The polished die-cast aluminum base and fixed ring armrests add an element of elegance and sophistication. Available with casters or glides. Vitra's AC 4 Task Chair has been awarded the Blue Angel eco-label and is also GREENGUARD Certified. AC 4 is made of up to 51% recycled materials and can be re-recycled up to 94%.