Porous thin-film dielectric insulators with significantly lower dielectric constants are expected to have great impact on the fabrication of ever smaller semiconductor devices and chips with higher packaging densities. Here two routes to the preparation of such nanoporous thin films are presented. A method has been developed that generates polyimide foams with nanopores from a block copolymer in which the dispersed phase undergoes thermolysis. The other approach described uses branched, highly functional macromolecules as molecular templates during vitrification of a siles-quioxane.