The smart textiles sector is becoming increasingly significant within the technical textiles industry, contributing an increasing number of products and applications using a number of different technologies. This research is concerned primarily with electrically conductive smart textiles and, for the purposes of this project, smart structures are considered to be electrically conductive components which can be used in conjunction with technical textiles in order to enhance their performance and properties. The term `smart textiles' defines materials with advanced responsive properties enabling them to sense, actuate and/or control and the primary aim of this research was to characterise commercially available conductive yarns in terms of their structure, composition and physical behaviour in relation to their electrical behaviour. The secondary aim was to manufacture an electrically conductive textile material that could act as a strain sensor with the aim of integrating them into or onto existing technical textile fabrics. A range of static, dynamic and cyclic mechanical-electrical tests were carried out on a number of commercially available conductive yarns, work which informed the decision to base further experimental work on the integration of Carbon Black particles and Carbon Nanotubes into Nylon 6.10 and extrude a monofilament using a standard melt spinning technique. Although the resultant yarns manufactured did not display the properties required, analysis of the CB and CNT properties, the conductive particle dispersion within the polymer matrix, the yarn structure and the manufacturing method all informed the development of the design paradigm. The resultant design paradigm developed highlights the most significant variables and parameters to take into consideration when designing a textile sensor, and suggests solutions that would result in successful sample production. The paradigm covers design solutions for the conductive particles, the polymer, the compounding method, yarn manufacturing parameters and the resultant yarn structure. Whilst the information contained therein is not exhaustive, this being due to the inherent multilevel complexity of designing a textile system, it acts as a guide for sensor development and may help circumvent costly and timely sample manufacturing errors.