According to Snorri Sturluson's work, Niflhel could be interpreted as the lowest level of Hel, but Niflhel and sometimes Hel are conflated with the concept of Niflheim, a term which originates with Sturluson.
Snorri Sturluson's account suggests that Niflhel might represent the most inferior level of Hel, yet it is sometimes confused with the concept of Niflheim, which Sturluson himself introduced.