The exhibition "Les Immatériaux" opened at the Centre Georges Pompidou in Paris on 28 March 1985 — almost four decades ago. The New Media Department of the Musée National d'Art Moderne at the Centre Pompidou has recently developed two online resources that facilitate the study of this seminal exhibition:

1. A comprehensive “Instrument de Recherche”, through which the scans of hundreds of archive documents and photographs can be accessed online:
https://bibliothequekandinsky.centrepompidou.fr/billets/publication-research-tool-les-immateriaux

(The research tool itself is only in French, but the explanation on this introductory page is in English, and much of the rest is self-explanatory; to access all files it is necessary to create a free online user account of the Biliothèque Kandinsky.)

2. A navigable, virtual 3D reconstruction of the exhibition "Les Immatériaux", developed together with the ZKM Karlsruhe, is available at
https://lesimmateriaux.beyondmatter.eu/

Here there is also a suite of texts in the section "About Les Immatériaux" (to be found at the bottom of the intro page), which offer a good introduction to the main aspects of the exhibition, including an easy-to-use interface for listening to the original soundtrack.
[This website seems to work best with Chrome and Safari, not Firefox.]

The catalogues (partly now also in an English translation) and other printed materials remain easily available on Monoskop:
https://monoskop.org/Les_Immatériaux