Accurate representations of real-world materials are a crucial prerequisite for realistic image synthesis. This thesis presents a method for rendering fabric based on a low-level simulation of light scattering from threads. Making use of reflectance acquisition techniques, we study the reflectance characteristics of a variety of threads extracted from real-world fabrics. We introduce a model for light scattering from threads which simulates both the surface and subsurface transport of light. The model's accuracy is assessed against physical measurements. In order to generate an image of fabric, we propose a weave pattern and thread curve encoding that enables us to mimic the structure of a wide variety of fabrics. We apply this appearance model in a path tracing framework to realistically reproduce the appearance of fabrics