Together with Pier Giacomo, in 1957 he designed “Sella” and “Mezzadro” stools for Zanotta, as well as the “Cubo” couch for Arflex. In 1959, they began working with Kartell, designing lighting and furniture, including a collection of tables and stools called “Rochetto”. The Castiglioni brothers designed the “Lierna” chair for Cassina, and the “Taraxacum” chandelier for Flos in 1960. Also for Flos, in 1962 they designed both the “Toio” lamp, assembled from “ready-made” surplus hardware, and the “Arco” lamp, consisting of a long-arched stainless-steel cantilevered support, an adjustable shade made of perforated spun aluminium, and a heavy marble base. These projects were followed in 1964 by the “Splüghen Braü” pendant light, and the “RR 126” radiogram for Brionvega.
From 1969 he taught architectural and design subjects, first at the Politecnico di Torino, and then, from 1980, at the Politecnico di Milano. As a professor of design, he advised his students, “If you are not curious, forget it. If you are not interested in others, what they do and how they act, then being a designer is not the right job for you.” Throughout his lifetime, Castiglioni received many awards and distinctions for his designs, including 8 x Compasso d’Oro, as well as the Compasso d’Oro Career Award “for having raised design to the highest values of culture through his irreplaceable experience.” His designs are held in museum collections around the world, and several books have been published about his life and work.