Refer to figure.

In contrast to a laminar layer, a turbulent boundary layer exhibits greater thickness and higher skin friction. With increased energy, it displays a reduced tendency to separate from the surface. This higher level of kinetic energy, results in the ability of a turbulent layer to follow a shape better than a laminar flow.

The thin laminar layer is highly responsive to surface irregularities. Any roughness on the leading portion of an aircraft's skin triggers a transition to turbulence at that point. This results in the thickening of the turbulent boundary layer, which fans out downstream and leads to a significant rise in skin friction drag.