Heavy Boobs is a collection of mods designed to increase the maximum size of breasts and improve their appearance.  It's primarily a slider mod, meaning it affects every outfit of every female Sim in the game.  Secondly, this mod adjusts several clothing meshes and adds some detail options.  The goal of Heavy Boobs is to give larger breasts a more weighty appearance; having them sag a bit with rounded undersides as well as adding indications of nipples poking into thinner fabric.