Pyen borrows more from Lahu and Shan, while Bisu borrows more from Northern Thai and Standard Thai. Pyen and Bisu are both mutually intelligible, since the two form a dialect chain along with Laomian and Laopin of China, and some Phunoi varieties of Laos (Person 2007).
- Pyen at Ethnologue (18th ed., 2015)
- Hammarström, Harald; Forkel, Robert; Haspelmath, Martin; Bank, Sebastian, eds. (2016). "Pyen". Glottolog 2.7. Jena: Max Planck Institute for the Science of Human History.
- Person, Kirk R. 2007. A preliminary phonological sketch of Pyen, with comparison to Bisu. Canberra: Pacific Linguistics.
- Shintani Tadahiko. 2009. The Pyen (or Phen) language: its classified lexicon. Fuchu (Tokyo-to): Research Institute for Languages and Cultures of Asia and Africa.