Reflectant chestplate is part of the unique reflectant armor set. This set is only obtainable after The Glass Wall quest has been completed, simiarly to the ghostly robes set, you must complete a post-quest minigame. The minigame is called glass cleaner, you have to help Jarraat, a creature who is very prone to sunlight by helping him keep his sun light reflecting barriers up bu helping him protect them from his enemies. You will receive this chestplate as a reward for helping Jarraat with the quest and helping him upkeep his glass barriers.