Cluster mass as a function of cluster size (full symbols) for exposed clusters more massive than 10³ M_⊙. The diamond symbols represent clusters younger than 4 Myr, the squares clusters in the age range 4 Myr  < t_c < 10 Myr, and the circles clusters with ages 10 Myr  < t_c < 20 Myr. The thick line shows that the cluster mass remains more or less constant for the starburst cluster sequence, whereas the leaky cluster mass rapidly declines with cluster age (thick dashed line). The values were taken from Figer (2008), Wolff et al. (2007), and Borissova et al. (2008). In addition, the relation between the cluster density and cluster radius are shown by empty symbols as in Pfalzner (2009).