The relative density of a polymer is due to branching factors mainly, right? So would it be correct to assume that thicker materials such as thick plastic sheets (for example) would be due to a polymer that is less branched (aks more “linear” of a structure) (Yes. - GS). whereas the plastic for packaging is more branched making it more flexible? (Flexibility is mostly determined by conformational mobility. - GS). Just out of curiosity, how would you go about manipulating this concept, so that you could produce a compound of desired density? (In industry, radical-induced polymerization of ethylene causes the radical centers hopping along the chain, which causes branching. Polymerization directed by a metal (Ziegler-Natta catalyst), produces mostly linear chains. An extreme example of this type of manipulation is making aerogels in supercritical carbon dioxide. - GS). Meaning if I were to say add heat to the compound/ substance the material would become more flexible? (Yes, which is why under freezing temperatures, some plastics and rubbers become inflexible, fragile, and may fall apart. It is a big issue for aircraft landing gear and spaceships. - GS).