A zephyrium bar is a bar of refined Zephyrium ore. It can be created through the Smithing skill by using zephyrium ore on a furnace, requiring level 50 Smithing and granting 38.5 Smithing experience. The zephyrium ore itself can be mined from the rocks scattered throughout the dungeon, obtained as a monster drop, or bought from the Smuggler.
A zephyrium bar can be smithed on an anvil through the Smithing skill to create Zephyrium equipment, granting between 55 and 59.5 Smithing experience per bar used. A list of zephyrium items that can be smithed from zephyrium bars and the Smithing levels required can be found here.
Five zephyrium bars are used along with 5 bovistrangler branches to build a Prayer altar in the hotspot located in the start room of a dungeon. This requires level 75 Construction.