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Background Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterised by progressive fibrosis. Environmental exposures, including fine particulate matter (PM 2.5), have been implicated in the progression of IPF; however, indoor data are limited. We aimed to evaluate the impact of indoor exposure to PM2.5 on the progression of IPF.Methods and analysis This prospective, multicentre cohort study involves 15 medical institutions across South Korea. A total of 120 patients with IPF have been recruited and will be followed for 1 year. The impact of indoor exposure to PM 2.5 on clinical outcomes, including progression of the disease (defined as a relative decline in forced vital capacity ≥10% or diffusing capacity for carbon monoxide ≥15%), hospitalisation, acute exacerbations and mortality, will be assessed. Pulmonary function tests will be conducted quarterly at institutions, with home-based spirometry performed daily in a subset of 50 participants. The indoor PM2.5 level will be continuously measured using a scattering-based indoor air quality monitor (IAQ-CL; KWeather, Seoul, South Korea) and PM10, volatile organic compounds and carbon dioxide will also be measured. Biomarker analysis of Krebs von den Lungen-6 and other related markers will be performed. Statistical analyses will use linear mixed-effects models and time-to-event models to evaluate the association between exposure to PM and clinical and biomarker outcomes.Ethics and dissemination The study has been approved by the Institutional Review Boards of all institutions, including Asan Medical Center (S2021-1136-0051). Written informed consent was obtained from all participants prior to enrolment.Trial registration number KCT0008638.