Armor versus archery

[Medicus matt]

Joinville was hit by five of those darts wearing nothing but his underarmour aketon and only received minor injuries.

Do you mean his description of the battle at Mansoora? If I recall correctly (don't have a copy to hand) Joinville writes that he found a Saracen 'oakum' tunic which he held in front of him as a shield. That worked well enough that he was only injured five times by 'fire-darts'.