Answer:
The answer is phospholipids.
Step-by-step explanation:
Phospholipids are lipids of which biological membranes are composed. A molecule of phospholipid is constituted by a phosphate group (which is polar, and can interact with water molecules) bonded to a glycerol molecule, which is bonded to two fatty acid chains (which are non polar molecules, and can interact each other). The phosphate group is the "hydrophilic head" and is located in the outer face of the membrane, whereas the fatty acids form the "hydrophobic tail" and it is in the inner face of the membrane, exposed to the aqueous environment. The structure resembles to a "hairpin": a head with a tail.