Normal capacitors have to have absurdly thin dielectrics to get any appreciable charge storage. An aluminium electrolytic capacitor (the can shaped ones) use ju

Normal capacitors have to have absurdly thin dielectrics to get any appreciable charge storage. An aluminium electrolytic capacitor (the can shaped ones) use just thickness of an aluminium oxide layer. Any sandwich thickness that would be practical for thermal insulation will have essentially zero capacitance. And even if you could have a super thin, delicate layer in the walls, and the builders don't break it putting it in, why not just roll it up tightly and put it safely in a can along with any electrolyte it needs in the first place? The key feature of supercapacitors is that they exploit 3D effects (or rather a 2D effect around very tiny features in a 3D volume) that allow them to use the volume of the material, combined with a very tiny effective charge separation.