Spiritbond is gained with a piece of gear as you accumulate Experience Points while wearing it (or if capped perform an action which otherwise would yield experience points). When spiritbond with a piece of gear reaches 100%, you can convert it into materia - if it is convertible and you have completed the prerequisite quest (called Forging the Spirit.) While all equippable items can be spiritbonded, "Non-convertible" items cannot be converted into materia.
HQ gear increases the rate of bonding by 20%. Each piece of materia bound to the gear being spiritbonded will also increase rate of bonding by +20%.
|I||i0 - i19|
|II/III||i30 - i44|
|III/IV||i45 - i69|
The materia tier is determined based upon the ilevel of the piece being converted. A minimum tier is guaranteed based on the iLevel of the gear being converted, but there is also an approximately 10% chance of obtaining the higher available tier.
The materia type is determined based upon the type of gear being converted, typically determined based upon the primary attributes of the item. There are four buckets of materia.