A technology for controlling the thermal conductivity of etch-released microstructures is proposed and demonstrated by placing test structures in and out of contact with their underlying substrate. By adjusting the duty cycle of a periodic actuation, the thermal conductivity can be adjusted linearly across a wide range. Experimental work with microfilaments in air has shown a continuous tuning range from approximately 1.7×10-4W/K to 3.3×10-4W/K. These numbers are limited by thermal conduction through air and thermal contact conductance, respectively. The fundamental tuning range is orders of magnitude wider, limited by radiation heat transfer and the thermal contact conductance of coated structures.