We have used a commercially available Mylar film coated with a thin (~60nm) layer of aluminium and an ultrathin (~3.5nm) SiO 2 layer as flexible substrate for the manufacture of bottom-gate organic field-effect transistors (OFETs). We show that the SiO 2 layer has insulating properties with a breakdown voltage of 1.6V and a capacitance of ~1μF/cm 2 . We have manufactured organic field-effect transistors using this substrate, regioregular poly(3-hexylthiophene) (rrP3HT) as a p-type semiconductor, and gold source and drain contacts. This results in OFETs that operate with voltages on the order 1V.