The durability for armor is broken, I believe since A17.
If I remember correctly, in A16 and bellow, the durability of the clothing also affected how efficient the clothes were. Like the durability of a tool used to affect it's stats.
With the new mods updates in A17 however, and the new durability system, things changed. The durability of an item doesn't affect how efficient that item is anymore.
All the clothes and armor do not have durability anymore.
That bar for armor is from tiers and doesn't serve any other purpose. Now its just a leftover from the old system.
I believe FunPimps weren't intending to make armor have no durability. But with the new system implied, they've forgot to adjust the armor.