A thin sensor for heat flux and temperature, designed for adhesive attachment to a surface, is manufactured on a flexible insulated metallic substrate. The sensor exhibits a combination of high sensitivity for heat flux and low resistance to the flow of heat. These characteristics enable it to measure heat flux at surface boundaries with improved accuracy over conventional heat flux transducers because the temperature drop produced by the sensor is very small. The response by the sensor to radiation, convection and conduction are equal. As such, the sensor can be calibrated in one mode of heat transfer and used for measurement in other modes. The high sensitivity of the sensor makes it ideal for measuring heat flow through insulating materials, and well adapted to instrumenting heat flow in buildings, detecting fires at an early stage, or remotely measuring the temperature of string and web products in industrial processing.