In our previous paper, the yarn-based sensors are shown capable of measuring the respiration signals. In comparing with fabric-based sensors, the yarn-based sensor is more comfortable in wearing, and easily fabricated by conventional textile process. In this paper, we aim at the analysis of the design parameters of the yarn-based sensors that were fabricated by double wrapping the polyester, ... [Show full abstract] elastic, and piezoresistive fibers. The performances of the yarn-based sensor under different compositions have been experimentally evaluated. It is shown that the soft-core yarn sensors achieve high gain factors with low linearity. The sensors consisting of high-density piezoresistive fibers achieve high linearity with low gain factor. It was also shown that the nonlinearity of the sensors that is mainly due to the irregular characteristics of the yarn structure exits at the low strain region. As at the high strain region, the high linearity of the yarn-based sensors is found regardless of material compositions. To further reduce irregular characteristics of the yarn structure, to increase the preload and to choose the stiffer core yarn and the harder piezoresistive fibers are suggested.