The rapid liberalization of tariff barriers has elevated non-tariff measures (NTMs) to a central role in shaping global textile and apparel trade, yet rigorous, Vietnam-specific analyses of how European Union (EU) NTMs under the EVFTA affect Vietnamese exporters remain scarce. This study fills that gap by combining novel indices—Degree of Application, Frequency of Application, and Effectiveness—built on UNCTAD’s taxonomy with detailed HS 61–63 trade-flow data (2012–2024) and semi-structured interviews of exporters and certifying bodies. We quantify the incidence and intensity of key EU NTMs (REACH, EU Ecolabel, “yarn-forward” rules) and estimate their differentiated impacts on export prices, volumes, and product composition across firm sizes. Our findings reveal that large enterprises securing sustainability certifications achieve 15–25 percent price premiums and sustained volume growth in premium segments, whereas SMEs face 8–12 percent MFN duties and market exclusion when origin rules are unmet. We also document a structural shift toward higher-value, eco-friendly products—organic-cotton and recycled-fiber lines—driven by evolving EU sustainability mandates. By integrating quantitative NTM metrics with firm-level insights, this research contributes to the literature on trade protectionism by providing the first comprehensive assessment of EVFTA-era NTMs on Vietnam’s apparel sector and offers concrete policy recommendations to transform compliance burdens into competitive advantages.