NanoPoly Resources LLC will establish a repository of and standardized manufacturing platform for environmentally relevant, weathered micro- and nanoplastic (MNP) reference materials. These reference materials—produced in realistic shapes, sizes, and aging states that mirror what is found in the environment, will be supplied to STOMP performers to ensure consistent, comparable measurements across teams and to underpin the program's measurement and mechanistic research. By supplying consistent reference materials to STOMP measurement (TA1) and mechanistic understanding (TA2) performers, this project establishes a shared foundation that enables cross-team comparability, rigorous method validation, and standardized dosing—critical prerequisites for accurately detecting MNPs in biological samples and illuminating how they traffic through and harm the human body.