A fat molecule is less soluble in water than a phospholipid molecule. This is because fats (triglycerides) are nonpolar and hydrophobic, meaning they do not attract water and are completely insoluble in it. In contrast, phospholipids are amphipathic molecules with both a hydrophilic (polar, water-attracting) "head" and hydrophobic (nonpolar) "tails." The polar head group of phospholipids interacts with water, making phospholipids partially soluble in water. This polarity allows phospholipids to form structures like bilayers in aqueous environments, whereas fats cannot dissolve in water due to their entirely hydrophobic nature.