Amaterial with a lower/higher r-value is a better insulator.

A material with a higher R-value is a better insulator.

The R-value is a measure of a material’s (such as a layer of insulation) resistance to conductive heat flow. Materials with higher R-value indicate better insulating properties or effectiveness. Certain factors such as the thickness, density and the type of insulation determine the R-value of most materials while for some insulation, it is also determined by aging, temperature and moisture accumulation.

not sure if this what   you'r looking for would be percent composition