Piwafwi is a drow word meaning cloak. Also, a (lesser or common) Piwafwi is an ordinary-looking drow dark woven magical cloak, much like a Cloak of Elvenkind. When the hood is drawn over the head, the wearer becomes almost invisible to normal sight, akin to an invisibility spell, and infravision, thanks to the heat-shielding properties of the cloak. The drow use these cloaks to stay out of sight in the Underdark. They are fashioned from spider silk and other unknown fibres and it is common for the wearer’s house symbol to be included on the cloak. Many Piwafwi especially those of Drow nobles or wizards are known to have other magical Enchantments on them that make them strong enough to be resistant to magical and melee attacks. 123
As with drow possessions in general, it is very rare for other races to have Piwafwis due to the xenophobic and protective nature of drow society.