Flexible and bio-compatible temperature sensors based on carbon nanotube composites

•We developed flexible temperature sensors based on carbon nanotube (CNT) forest composites.•The operational principle relies on the thermal mismatch between the CNTs and the filler.•The sensors demonstrate simple sensing scheme and excellent sensitivity of ~0.1 Ω/°C.•The sensors exhibit high reproducibility under sequential thermal loads.•The sensors are bio-compatible, as on-skin temperature sensing was demonstrated.