Objectives <p>To compare polymerization shrinkage and shrinkage stress of highly filled flowable resin composites with conventional low filled and bulk-fill flowables.</p> Materials and methods <p>Fifteen flowable resin composites with A2-shade were tested. For each material, shrinkage depth (µm) was measured using a topography-based cavity method (<i>n</i> = 10), and peak polymerization shrinkage stress (MPa) using a bonded-disc test (<i>n</i> = 5) under a standardized light-curing protocol. Data were analyzed with one-way ANOVA, Tukey’s post-hoc tests, and Pearson’s correlations.</p> Results <p>Shrinkage depth ranged from 84.08 ± 14.66&#xa0;μm to 169.81 ± 6.93&#xa0;μm, whereas stress ranged from 2.84 ± 0.28&#xa0;MPa to 6.34 ± 0.56&#xa0;MPa. Shrinkage and stress were negatively correlated (<i>r</i> = − 0.749, <i>p</i> = 0.0013). “Bulk-fill” status showed no association with shrinkage stress (<i>r</i> = − 0.136, <i>p</i> = 0.628) or shrinkage depth (<i>r</i> = 0.199, <i>p</i> = 0.476).</p> Conclusions <p>Highly filled flowables tended to reduce shrinkage but often developed higher stress, whereas some low filled bulk-fills reduced stress despite higher shrinkage. Shrinkage and stress should be considered independently, as material category labels and viscosity classes are not reliable predictors of material behavior.</p> Clinical relevance <p>Polymerization shrinkage and peak shrinkage stress varied markedly among both low filled and highly-filled flowable composites, and the ‘bulk-fill’ designation was not a reliable predictor of either outcome. Clinicians should therefore select materials according to their specific shrinkage and stress profiles in relation to cavity geometry, rather than relying solely on category labels, especially when maintaining interfacial integrity is critical.</p> Clinical trial registration <p>Not applicable.</p>