Phospholipids form the main fabric of the plasma membrane. one feature of phospholipids is that when they are placed in an aqueous solution, they will self-assemble into a double layer (bilayer) that resembles the bilayer of the plasma membrane. this self-assembly occurs because phospholipids are hydrophilic at one end (the phospholipid head) and hydrophobic at the other end (the phospholipid tails).

The bilayer is structured in such a way that it complements the extracellular fluid around the cell as well as the cytoplasm within the cell. This is because the extracellular fluid is hydrophillic, the outside of the membrane protein is hydrophillic, the middle of the membrane protein is hydrophobic, the inside of the cell (the cytoplasm) is hydrophillic and the inside of the membrane protein is hydrophillic.