How are hydrophilic phospholipid heads arranged in a cell membrane?

In a cell membrane, the hydrophilic (water-soluble) phospholipid heads are arranged to face outward into the surrounding water medium.1

Because these molecules are amphiphilic, they spontaneously organize into a lipid bilayer to satisfy their chemical affinities. In this structure:1

• The water-repellent, lipid-soluble tails are sequestered in the interior of the membrane, where they bond with the tails of the opposing sheet.1
• The hydrophilic heads are oriented toward the aqueous environment on both the exterior and interior sides of the cell, where they are chemically attracted to water.1

This arrangement creates a stable, fluid, sandwich-like structure that effectively separates the cell's internal environment from the outside.1