Left: dust formation rate diagram: sM_dust vs. sSFR in the Hi-z LBGs (red data points). Only models with a delayed star formation history are plotted. Consistently, a delayed star formation history only was used in the SED fitting with CIGALE to estimate sM_dust and sSFR. The models shown do not have any grain growth in the ISM. We select the best models (shown in blue) by computing the χ² of the models with respect to sM_dust, sSFR, and age, and finally use the combined total χ² as quality of the fit to select the best models. We also plot the other models in light grey to plot which parameter space the models cover. Right: specific dust mass vs. age of the dominant stellar population. Models with a larger condensation fraction provide better fits, on average. The Hi-z LBGs are young galaxies. The steep decline of sM_dust for Hi-z LBGs with respect to Low-zZ galaxies suggest a fast removal (destruction + outflow) of grains in about 0.5 Gyr for Hi-z LBGs that can explain the various detectability of these Hi-z LBGs. Colours have the same meaning as in the left panel.