The hydrophobic part of a phospholipid is its fatty acid tails. These tails are made of long chains of carbon and hydrogen atoms, which are nonpolar and do not interact well with water, causing them to repel water. In contrast, the phosphate-containing head of the phospholipid is hydrophilic, meaning it is attracted to water. Thus, in a phospholipid bilayer, the hydrophobic fatty acid tails face inward, away from water, while the hydrophilic heads face outward toward the aqueous environment.