Flexible thermal links are necessary to couple thermally but flexibly instrument sensors to their heat sink. Three promising flexible thermal link design concepts are described and investigated, the braided solid conductor made of metallic foils, the spring-shaped axial grooved heat pipe and the carbon fibre thermal link. The design principles of those concepts are presented. Advantages, drawbacks and critical points are analyzed and typical performance data are reported. This work includes also results from mechanical and thermal tests performed on various flexible thermal link samples.The investigations reveal, that braided metallic conductors can cover the widest range of applications. However, for a certain range of applications, the spring-shaped heat pipe and the carbon fibre link are valid alternatives with significant improvement of the thermal conductance associated with lower mass and similar mechanical performance.