Series I. Research contains material gathered by Day relating to his research interests in knots. This series contains two subseries.

Subseries A. Articles, Notes, and Related Correspondence contains research materials collected by Day. The folders, organized by topic, consist of a variety of journal articles, notes about his research, or on particular articles, photographs, sketches, and correspondence. The material has been kept in the original order imposed by Day. Not all of the material is in English.

Subseries B. Illustrations and Photostats contains a folder that Day labeled "Illustrations" which contains illustrations, photographs, notes about images, articles, and research notes. This series also contains photostats of images, some of which appear in the book Quipus and Witches' Knots: the Role of the Knot in Primitive and Ancient Cultures. There are also page proofs of the photostats.