> [!abstract] Summary > Arnold's **Standard Hair** shader is the recommended solution for rendering hair and fur. Use curves in **ribbon mode**. Color is best driven by the **melanin** controls rather than a direct color input. For light-colored hair, increase specular samples to reduce noise. --- # Standard Hair ## Curve Mode > [!tip] When rendering hair, use curves in **ribbon** mode for best results with the Standard Hair shader. --- ## Color: Melanin vs Texture There are two ways to control hair color: ### Option 1 — Melanin Leave `base_color` as pure white and use the **melanin** controls instead. Melanin simulates physical light absorption inside the hair fiber and produces more realistic results than a flat color input. > [!note] Base color controls light **absorption** inside the fiber, which is what gives hair its appearance. Driving it directly with a texture bypasses the physical model — use melanin for realism. ### Option 2 — Texture - Set `melanin` to `0` - Connect your texture directly to `base_color` - Use a **ramp on V** to blend from root to tip color --- ## Melanin Randomize Adds per-strand variation to the melanin value, producing more natural-looking hair with slight color differences between strands. ![[file-20250126174214473.png|625]] --- ## Roughness Controls the overall glossiness of the hair. Lower values produce shinier, more specular hair; higher values produce a more diffuse, matte look. ![[file-20250126174246881.png|625]] --- ## Azimuthal Roughness > [!note] Only active when **Anisotropic Roughness** is enabled. Controls how rays travel laterally inside the hair shaft. A lower value lets rays pass straight through (sharper highlights), while a higher value scatters them more (softer, broader response). Intensity decreases as azimuthal roughness increases.  | 0.2 (default) | 1.0 | |---|---| ||| --- ## Shift Tilts the hair cuticle angle. For realistic **human hair**, use a small angle between **0° and 10°**. ![[file-20250126174535406.png]] --- ## Specular Tint Specular tint parameters act as **multipliers** on the specular color — they do not add color, they tint the existing specular response. --- ## Diffuse Standard Hair has no significant diffuse component by design, as real hair appearance is dominated by specular interactions. However, adding a small amount of diffuse can simulate **damaged or dry hair**. --- ## Rendering Tips > [!warning] Light-colored hair (blonde, white, grey) produces significantly more specular energy and will be noisier. Increase **specular samples** specifically for these cases. ![[file-20250126173929338.png]] - For light-colored hair: increase specular samples in the Arnold render settings - Use [[RaySwitch]] to assign a cheaper shader to indirect rays if hair is in the background or has many bounces - Ribbon curves generally give cleaner AA on hair strands than tube curves