When rendering objects with hardware tessellation, back-facing patches should be culled as early as possible to avoid unnecessary surface evaluations, and setup costs for the tessellator and rasterizer. For dynamic objects the popular cone-of-normals approach is usually approximated using tangent and bitangent cones. This is faster to compute, but less effective. We present a novel approach using the convex hull of the parametric tangent plane. It is much more accurate, and by operating in clip space we are able to reduce the computational cost significantly. As our algorithm vectorizes well, we observe comparable test times with increased cull-rates.