The cell membrane is composed of a phospholipid bilayer.
The cell membrane is primarily composed of a mix of proteins and phospholipids
Phospholipids are a major component of cell membranes. They a head and a tail. The head is hydrophilic (attracted to water) and the tail is hydrophobic (repelled by water).
They form a bilayer in which their hydrophilic heads face the aqueous cytosol and extracellular fluid while their hydrophobic tails face away from the cytosol and extracellular fluid.
The lipid bilayer is semi - permeable