The Microplastic (MP) SPR frameworks were developed for a typical urban sewage management context in Southeast Asia (SEA) and subsequently adapted to the practical environmental management conditions of three study cities: Bangkok Metropolitan Administration (BMA), Ho Chi Minh City (HCMC), and Jakarta (JKT). These frameworks identify five primary sources of MP pollution: domestic sewage, industrial wastewater, atmospheric deposition, agricultural runoff, and livestock wastewater. The major pathways within urban systems include stormwater runoff, transport through sewer networks, and wastewater treatment plants. The key endpoints of MP accumulation were defined and quantified as retention on land surfaces, discharge into surface water bodies, and deposition with sludge. This document outlines the underlying assumptions used in establishing the MP SPR framework for Southeast Asian cities, presents the tailored frameworks for the study cities, and details the MP flux flowcharts that trace flows from each primary source through identified pathways to their respective endpoints. It further describes the MP mass balance models and specifies the data requirements and outputs for quantifying MP influxes.