For the time being use GGX LTC table for hair.

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -355,6 +355,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - When a ray hits the sky in the ray marching part of mixed ray tracing, it is considered a miss.
 - TAA jitter is disabled while using Frame Debugger now.
 - Depth of field at half or quarter resolution is now computed consistently with the full resolution option (case 1335687).
+- Hair uses GGX LTC for area light specular.
 
 ## [11.0.0] - 2020-10-21
 

com.unity.render-pipelines.high-definition/Runtime/Material/Hair/Hair.hlsl

@@ -336,7 +336,9 @@ PreLightData GetPreLightData(float3 V, PositionInputs posInput, inout BSDFData b
     // Note we load the matrix transpose (avoid to have to transpose it in shader)
     preLightData.ltcTransformSpecular      = 0.0;
     preLightData.ltcTransformSpecular._m22 = 1.0;
-    preLightData.ltcTransformSpecular._m00_m02_m11_m20 = SAMPLE_TEXTURE2D_ARRAY_LOD(_LtcData, s_linear_clamp_sampler, uv, LTCLIGHTINGMODEL_KAJIYA_KAY_SPECULAR, 0);
+    // IMPORTANT NOTE: For the time being, until we solve issues with Kajiya Kay anisotropy and LTC tables, hair will fall-back on GGX.
+    // To be replaced with LTCLIGHTINGMODEL_KAJIYA_KAY_SPECULAR when that table is going to be valid.
+    preLightData.ltcTransformSpecular._m00_m02_m11_m20 = SAMPLE_TEXTURE2D_ARRAY_LOD(_LtcData, s_linear_clamp_sampler, uv, LTCLIGHTINGMODEL_GGX, 0);
 
     // Construct a right-handed view-dependent orthogonal basis around the normal
     preLightData.orthoBasisViewNormal = GetOrthoBasisViewNormal(V, N, preLightData.NdotV);