Thunderforged is a new sub-type of raid item drop quality introduced with Patch 5.2 in the Throne of Thunder raid. Each Patch 5.2 raid boss will have a chance of dropping this new designation of a particular item that's 6 item levels higher than their counterparts. Thunderforged items will drop more frequently in 25-player raids. Tier 15 armor pieces won't be available in Thunderforged quality at all.
Example item levels
- LFR quality at item level 502.
- Normal mode quality at item level 522.
- Normal mode Thunderforged quality at item level 528.
- Heroic mode quality of the item at level 535.
- Heroic mode Thunderforged version of the item at level 541.
- ^ a b c Crithto. #1 - 10- & 25-Player Raid Loot Changes – Patch 5.2. Official Community > General Discussion forum (US).