In folklore, mythology and fairy tales, a cloak of invisibility appears either as a magical item used by duplicitous characters or an item worn by a hero to fulfill a quest. It is a common theme in Welsh and Germanic folklore, and may originate with the cap of invisibility seen in ancient Greek myths. The motif falls under “D1361.12 magic cloak of invisibility” in the Stith Thompson motif index scheme. […]
The cloak in German fairy tales may be traceable to the tarnkappe (“cloak of concealment”),[5] such as the one that the hero Sîfrit (Siegfried) acquires from the dwarf Alberich in the Middle High German epic Nibelungenlied.[7] The Grimms clarify that Sîfrit’s kappe is a cape that covers not just the head but enshrouds the body, though in later times tarnkappe came to be regarded as a cap of invisibility.
Source: Cloak of invisibility – Wikipedia
Tim B.
“13 The Mantle of Arthur in Cornwall (Llen Arthyr yng Nghernyw): whoever was under it could not be seen, and he could see everyone.”
https://en.wikipedia.org/wiki/Thirteen_Treasures_of_the_Island_of_Britain