These are designs discovered during an autonomous experimentation campaign as detailed in:
Kelsey L. Snapp; Benjamin Verdier; Aldair E. Gongora; Samuel Silverman; Adedire D. Adesiji; Elise F. Morgan; Timothy J. Lawton; Emily Whiting; Keith A. Brown, Superlative mechanical energy absorbing efficiency discovered through self-driving lab-human partnership. Nat. Commun. 2024, 15 (1), 4290.
https://www.nature.com/articles/s41467-024-48534-4

They have excellent energy absorbing efficiency, meaning that their stress-strain or force-displacement curves are very flat when tested in compression.

Willow is predicted to function best when printed with a rigid plastic like PLA and Iroko is predicted to function best when printed as a flexible material such as Cheetah from Ninjatek.

The final parts should be shells, but included stls are both solid and shell files. The suggested method is to use to shell files and print in vase or spiral model.