Kalapa or rupa-kalapa (from Sanskrit rūpa "form, phenomenon" and kalāpa "bundle") is a term in Theravada Buddhist phenomenology for the smallest units of physical matter, said to be about 1/46,656th the size of a particle of dust from a wheel of chariot.
[1] Kalapas are not mentioned in the earliest Buddhists texts, such as the Tripitaka, but only in the Abhidhammattha-sangaha, an Abhidhamma commentary dated to the 11th or 12th century, and as such not part of common Theravada doctrine.
[2] According to the description found in the Abhidhammattha-sangaha, Kalapas are said to be invisible under normal circumstances but visible as a result of meditative samadhi.
[3] Kalapas are composed of eight inseparable elements of material essence in varying amounts which are:[4] Pathavi (earth), Apo (water), Tejo (fire), Vayo (air), Vanna (color), Gandha (smell), Rasa (taste), and Oja (nutrition).
[10][11][12][13] Mahasi Sayadaw in the 1980s expressed a belief that kalapas played a role in aging, death and rebirth.