NPCs will (usually
) help you out if their faction is set up so that you are allied to them (+1000 or greater).
As for armour materials, this is the list from armorpatterns.txt in the EQEmuAdmin directory -
0 Armor (cloth)
1 Armor (leather)
2 Armor (chain)
3 Armor (plate)
4 Armor (monk)
5 Armor (chitin)
7 Armor (scale)
10 Robe (advisor pattern)
11 Robe (FBR pattern)
12 Robe (ishva pattern)
13 Robe (oracle pattern)
14 Robe (kedge pattern)
15 Robe (SMR pattern)
16 Robe (plain)
17 Armor (icy)
18 Armor (dragonskin)
19 Armor (stability pattern)
20 Armor (ulthork)
21 Armor (ry'gorr pattern)
22 Armor (guardian pattern)