I printed this is some (10 year old?) Ninjaflex TPU. Designed on OnShape (https://cad.onshape.com/documents/a611d8e1063db7204149c00f/w/7fa394afcefe1b25e4fb7ead/e/b9e81badcf51a4d9dd3cad0d?renderMode=0&uiState=669b70b966460220ce7f14a8).
The author marked this model as their own original creation.