3D models are subject to a wide variety of processing operations such as compression, simplification or watermarking, which introduce slight geometric modifications on the shape. The main issue is to maximize the compression/simplification ratio or the watermark strength while minimizing these visual degradations. However few algorithms exploit the human visual system to hide these degradations, while perceptual attributes could be quite relevant for this task. Particularly, the Masking Effect defines the fact that a signal can be masked by the presence of another signal with similar frequency or orientation. In this context we introduce the notion of roughness for a 3D mesh, as a local measure of geometric noise on the surface. Indeed, a textured (or rough} region is able to hide geometric distortions much better than a smooth one. Our measure is based on curvature analysis on local windows of the mesh and is independent of the resolution/connectivity of the object. An application to Visual Masking is presented and discussed.