The cell membrane is produced of lipids, proteins and carbohydrates.

The membrane lipids are phospholipids, a particular type of lipid to which one extremity a phosphate group is bound therefore assigning electric charge to this region of the molecule. As phospholipids have one electric charged extremity and a long neutral organic chain they can organize themselves in two layers of associated molecules: the hydrophilic portion (polar) of every layer faces outwards in contact with water (a polar molecule too) of the extracellular and the intracellular space and the hydrophobic chains (non polar) faces inwards isolated from the water. Because this type of membrane is made of two phospolipid layers it is also known as bilipid membrane.