The main difference between LDL and HDL is their compositions. Approximately 50 percent of the weight of an LDL particle is cholesterol and only 25 percent is protein. High-density lipoprotein particles, on the other hand, consist of 20 percent cholesterol by weight and 50 percent protein. Since protein is more dense than fat, HDL particles are more dense than LDL particles, hence the names "high-density" and "low-density" lipoproteins. The structural difference between HDL and LDL particles is determined by the types of proteins in the molecule.