Nextbigfuture wrote this material which has been made in a chinese lab. The material is 20 times stronger than Kevlar.
Adam Crowl indicates super flywheels would be better than rocket fuel when oxygen is factored
For carbon nanotube material, with a density of about 1,800 kg/m3, and an operating maximum stress of 54 GPa, that means a specific energy density of 7.5 MJ/kg. For comparison a kilogram of natural gas represents about 50 MJ of chemical energy, if fully burned. However that comparison neglects the efficiency that the chemical energy can be turned into useful work. Flywheels convert their stored energy into electricity at very high efficiency – 95% or so. Running a gas powered generator turns maybe 20% of the gas's chemical energy into electrical energy.