Giant Spider Silk
Giant Spider Silk is a type of silk that comes from giant spiders and some related exotic insects. The threads of this material are larger and far stronger than conventional silk. While normal silk is already very effective in making cloth armor, this is the best possible material for that type of protection.
In Celestia this material is not exactly rare, but they can’t be farmed easily like silk worms. This makes it very expensive, though Players who know where to go can usually farm up a good amount of the material for their own crafting use.