In this paper, we propose a bit-allocation algorithm to transmit textured 3D models over low bit-rate channels. Both the geometry and the texture are progressively and independently compressed. Distribution of the bit budget between mesh and texture is based on a novel distortion measure, which quantifies the perceptual difference resulting from simplifying the geometry or using a low-resolution image or both. Using this distortion measure, we perform a rate-distortion optimized bit allocation to maximize the quality of the displayed model under a bit-rate constraint. The presented framework can be applied to any textured 3D models. Experimental results show that the proposed bit-allocation algorithm maximizes the visual quality of the textured model when it is transmitted over a low bit-rate channel.