The answer is: The polar heads interact with water; the nonpolar tails do not.
Phospholipids are a class of lipids and a significant component of all cell membranes. They are amphipathic molecules which means that they have a head that is hydrophilic (attracts water) and a tail that is hydrophobic (it repels water). The hydrophilic head has a negatively charged phosphate group, which is polar and which makes it hydrophilic. The hydrophobic tail typically consists of long fatty acid carbonic hydrogen chains. As a result, phosphates in water always turn to water and fatty acids to each other. In this way, a bilayer of phospholipid is formed which in the construction of the cell membrane prevents the release of the liquid content.
