There are a bit more information on his website [1] and I've made a temporary grouped BOM [2] :

    [1] https://la3emedim.fr/assets/SMALLEST%20-%20README.pdf  
    [2] https://docs.google.com/spreadsheets/d/1XXZB4jRtvtlDIqlR69C0FRri8x8lZDpxO6ZGnSp3L2Y/view

Basically anything but PLA will work, PETG will be the best difficulty/cost compromise.