Hair Realtime Primitive
Minimal
When you render hairs, most times there are a lot of them to render.
Shadows
For shadows a tube represantation is better then stripes because the shader will not disappear because the light source can be occluded by a tube from every side.
Approximation
To gain perfomance the tube can be reduced to have a triangular crosssection. For shading the normals can be smoothed out.
Normals
Normals for smoothed shading can be easily calculated through the crosssection points.