Which substances have the highest and lowest specific heat capacities?

The main determination of heat capacity is its molecular weight. Hydrogen has a low molecular weight and in turn has a very high heat capacity [c=14.307 J/gK]. Hydrogen isn't practical for uses as an insulator though. Styrofoam and many ceramics are quite heat resistant, but the best "insulator" is actually a total vacuum. Gold, being a heavy metal, has a very low heat capacity [c=0.128 J/gK]. Radon also has a very high molecular weight, and has a heat capacity of just 0.09 J/gK. I'm not certain that these are the highest and lowest heat capacities of all substances, but they are the highest and lowest of all the elements.

Interesting, Aloho. I have just read that any fluid at its vapour-liquid critical point has an infinite SHC. But hydrogenn is still looking like a good contender.
I'm unsure about the lowest.

With regards to elements:

This chart shows Technetium having the lowest heat capacity at 63 J/(Kg K)

Hydrogen has the highest heat capacity with 14300 J/(Kg K)

http://periodictable.com/Properties/A/SpecificHeat.al.html