Here's an article about leather armors: https://www.archeologiedordrecht.nl/wijkensites.dordrecht/up/ZwljtisJE_Leather_in_Warfare_Late-medieval_leather_armour_from_excavations_in_the_Netherlands_Marloes_Rijkelijkhuizen_and_Marquita_Volken.pdf
I had an article about cuirboulli helmets too, but unfortunately I can't find it, I may have lost it a while ago in a hd crash. I've read some other articles too, and looks like that cuirboulli wasn't as sturdy as it is in RQ, and no one used just cuirboulli armor, but it was used on top of other armors. And it wasn't a poor man's substitute for a metal armor.