From the book "Diane Arbus Revelations", p. 273:
She had tried all the film types available in the United States, and had made it very clear to me that she disliked them relative to the films of the two German manufacturers.... She resorted to pressing friends and acquaintance into buying Agfa IF for her in Germany and bringing it back with them.
The film was described as "ASA 50", "slow, silver-heavy Agla films".
Arbus shot 35mm until 1963, so it is possible she used other brands for the 35mm work. Later she used 120 film, shooting square negatives with a wide-angle Rolleiflex and a twin-lens Mamiyaflex, p. 270.