The interior portion of the cell membrane that is not exposed to the inner cytoplasm or the extracellular matrix is hydrophobic. Phospholipid molecules, which are composed of a hydrophilic head and two hydrophobic tails, make up the major component of the cell membrane. The heads are arranged in such a way as to form a hydrophilic outer lining facing the extracellular matrix and a hydrophilic inner lining facing the aqueous cytoplasm. The tails lie sandwiched in between the outer and inner lining, creating a hydrophobic interior region. Water is attracted to the surfaces of the membrane but is unable to pass through the hydrophobic interior layer.