Have you looked into nano material (e.g. nano carbon). There's a really strong flexible material that outclasses Kevlar, I can't remember its name off the tongue (It's definitely a carbon structure though).
Have you thought about inventing your own material? You could have a material made from carbon and helium molecules. The idea being the helium would draw the carbon closer to one another giving the material a greater density; of course, the only problem would be explaining how helium was forced to share its electrons without completely separating. You could possibly use a bit of science fiction with a less than scientific application of dark matter, so you could use dark matter's macroscopic theoretical influence on a microscopic scale to force the helium to remain in the exact same position where the carbons could possibly have enough of an electrostatic force to strip the helium for a second in a dipole-dipole convalent bond (and I mean in terms of science fiction, in real life that helium would've [spoiler]fucked[/spoiler] off before I even spoke the first syllable).
Have you thought about inventing your own material? You could have a material made from carbon and helium molecules. The idea being the helium would draw the carbon closer to one another giving the material a greater density; of course, the only problem would be explaining how helium was forced to share its electrons without completely separating. You could possibly use a bit of science fiction with a less than scientific application of dark matter, so you could use dark matter's macroscopic theoretical influence on a microscopic scale to force the helium to remain in the exact same position where the carbons could possibly have enough of an electrostatic force to strip the helium for a second in a dipole-dipole convalent bond (and I mean in terms of science fiction, in real life that helium would've [spoiler]fucked[/spoiler] off before I even spoke the first syllable).