bilayer

This term is primarily used in scientific and technical registers, particularly in biochemistry, materials science, and nanotechnology. It describes a specific structural arrangement where two distinct layers are bonded or stacked. In biological contexts, it almost exclusively refers to the phospholipid bilayer of cell membranes, where hydrophobic tails face inward and hydrophilic heads face outward.

When used as an adjective, it modifies a noun to specify the composition of a material or coating, such as a bilayer film. While the noun form is common in academic literature, the adjective form is more frequent in engineering and industrial applications to describe the physical architecture of a component.