I have not seen this discussed on here but if it has , I apologize for the repeat. Looking at the densities of various polyethylenes, one can arrive at some knowledge of the structure of those polymers, with significant branching causing, generally, a reduction in density. I am curious if anyone has tried to correlate overall density of a lubricating oil to the percentage of PAO, Type III, etc. Some of the syn oils have a very low density, it seems. Any thoughts on this??