Which type of molecule makes up the double layer of a cell membrane?

The double layers of cell membranes is made up of PHOSPHOLIPIDS.

The cell membrane, also called plasma membrane is made up of double layers of phospholipids. Phospholipid is a type of lipid, which is made up of two parts, an hydrophillic head and a hydrophobic tail. The hydrophillic head is made up of phosphate and glyerol while the hydrophobic tail is made up of fatty acids. The double layer of phospholipids serves as a barrier that allows only certain substances to enter into the cells.

a physical change is being made.