OBJECTIVE: A new type of so-called 'packable', 'condensable' or 'mouldable' composite has been developed and aims at replacing amalgam for posterior restorations. The purpose of the present investigation was to study the dynamic elastic modulus of 12 packable composites, and to follow the evolution of this property following prolonged water absorption. METHODS: Of each material ten rectangular samples (1.5x5x35 mm) were prepared. The elastic modulus (GPa) of each sample was determined with a non-destructive dynamic method using a Grindo-Sonic after 24 h of dry storage at room temperature, and after 24h, 1, 3 and 6 months of wet storage at 37 degrees C. All data were analyzed using two-way ANOVA, Bonferroni/Dunn's test for multiple comparisons and paired t-test with a significance level of p<0.05. In addition, inorganic filler volume percentages were derived from the phenomenological model introduced by Braem et al. . RESULTS: The studied materials varied widely in terms of elastic modulus, ranging between composites classified as Compact-Filled Densified (elastic modulus of 23.4+/-2.4 GPa) and as Microfine (elastic modulus of 8.5+/-2.1 GPa). SIGNIFICANCE: The great diversity observed in the elastic modulus of this type of composites necessitates clear specifications with regard to 'first' the definition of marketing terms such as packable and so on, and 'second' the justified use in posterior teeth.