Dense and porous hyperbranched carbosiloxane thin films (HBCSO) are obtained by sol-gel processing using methylene-bridged hyperbranched polycarbosilanes (HBPCSs) with the general compositional formula {(OMe)(2)Si(CH2)}. Introduction of porosity is achieved using a porogen templating approach, allowing the control of the films' dielectric constant from 2.9 to as low as 1.8. Over the entire dielectric range, the HBCSO films exhibit exceptional mechanical properties, 2-3 times superior to those obtained for non-alkylene bridged organosiloxanes such as methylsilsesquioxanes (MSSQs) of similar densities and k-values.