This study reports mesoscopic thermal transport measurements of individual multiwalled carbon nanotubes (MWNTs). The thermal conductivity of a single MWNT was measured to be over 3000 W/m·K at room temperature, which is two orders of magnitude higher than previous bulk measurements. The thermal conductivity exhibits a peak at 320 K due to Umklapp phonon scattering. The thermoelectric power (TEP) shows a linear temperature dependence with a value of 80 μV/K at room temperature. The researchers developed a microfabricated suspended device to measure thermal transport without substrate contact. The device consists of two suspended islands connected by a MWNT. A heater resistor and a sensor resistor were used to measure temperature changes. The thermal conductance of the MWNT was calculated using a heat transfer model. The measured thermal conductance includes contributions from the junction between the MWNT and the islands, as well as the intrinsic thermal conductance of the MWNT itself. The thermal conductivity of the MWNT was found to increase with temperature, reaching a maximum near room temperature before decreasing at higher temperatures. The temperature dependence of the thermal conductivity showed a crossover from a T^2.5 dependence at low temperatures to a T^2 dependence at higher temperatures, indicating a transition from three-dimensional to two-dimensional thermal conduction. The phonon mean free path was estimated to be approximately 500 nm. The TEP of the MWNT was measured to be linear with temperature, with a value of 80 μV/K at room temperature. This is in agreement with theoretical predictions for metallic and doped semiconducting nanotubes. The results suggest that the intrinsic thermal properties of individual nanotubes are significantly different from those of bulk samples, which are dominated by thermal junctions between tubes. The study highlights the importance of mesoscopic measurements for understanding the thermal properties of nanotubes. The experimental techniques developed can be applied to other nanoscale materials to study their thermal properties. The results provide new insights into the thermal behavior of carbon nanotubes and their potential applications in nanotechnology.This study reports mesoscopic thermal transport measurements of individual multiwalled carbon nanotubes (MWNTs). The thermal conductivity of a single MWNT was measured to be over 3000 W/m·K at room temperature, which is two orders of magnitude higher than previous bulk measurements. The thermal conductivity exhibits a peak at 320 K due to Umklapp phonon scattering. The thermoelectric power (TEP) shows a linear temperature dependence with a value of 80 μV/K at room temperature. The researchers developed a microfabricated suspended device to measure thermal transport without substrate contact. The device consists of two suspended islands connected by a MWNT. A heater resistor and a sensor resistor were used to measure temperature changes. The thermal conductance of the MWNT was calculated using a heat transfer model. The measured thermal conductance includes contributions from the junction between the MWNT and the islands, as well as the intrinsic thermal conductance of the MWNT itself. The thermal conductivity of the MWNT was found to increase with temperature, reaching a maximum near room temperature before decreasing at higher temperatures. The temperature dependence of the thermal conductivity showed a crossover from a T^2.5 dependence at low temperatures to a T^2 dependence at higher temperatures, indicating a transition from three-dimensional to two-dimensional thermal conduction. The phonon mean free path was estimated to be approximately 500 nm. The TEP of the MWNT was measured to be linear with temperature, with a value of 80 μV/K at room temperature. This is in agreement with theoretical predictions for metallic and doped semiconducting nanotubes. The results suggest that the intrinsic thermal properties of individual nanotubes are significantly different from those of bulk samples, which are dominated by thermal junctions between tubes. The study highlights the importance of mesoscopic measurements for understanding the thermal properties of nanotubes. The experimental techniques developed can be applied to other nanoscale materials to study their thermal properties. The results provide new insights into the thermal behavior of carbon nanotubes and their potential applications in nanotechnology.