bendy ply
https://plydirect.co.uk/product/fle...MIiLzu06rjgwMVJ6ODBx3k8wIbEAQYByABEgJCdvD_BwEI seem to remember another product, we used it in college. I think(dont quote me) that that was flexible in long or cross grain orientation. Depending on the project you would specify one or the other. That was thinner than the 5 or 8mm in the link above. Cant remember exactly, but maybe 2 or 3mm.
Example of use would be in a former, X number of sheets to the required thickness, then a final standard thickness 0.6mm veneer sheet as a final finished surface. So if you wanted to do something like an Eames chair, you use the bendy for the core material, then a rosewood(or whatever) front and back layer to create the shells.