The process in which a relatively unspecialized cell acquires specialized features of a type I pneumocyte. A type I pneumocyte is a flattened cell with greatly attenuated cytoplasm and a paucity of organelles. [ GOC:mtg_lung GOC:dph https://www.worldcat.org/search?q=bn%3A0721662544 ]
Synonyms: membranous pneumocyte differentiation