A novel flexible pulsating heat pipe technology (FPHP) is presented, which enables fabrication of flexible, lightweight and low cost heat transfer devices using thermoplastic materials (polypropylene). A flexible and lightweight PHP is advantageous for space, aircraft and portable electronic applications where the device weight is crucial. Although the thermal performance of thermoplastics is usually poor, this technology enables the creation of composite thermoplastic materials having a significantly enhanced thermal conductivity. The basic concept is to sandwich a serpentine channel, which is cut out in a polypropylene sheet and contains a self-propelled gas-vapour mixture, between two transparent polypropylene sheets, bonded together by selective laser welding. This results into a heat transfer device with a large surface and very small thickness (approximately 1.5 mm), which makes it suitable for many existing and future applications where thermal management is not possible using existing technologies. The thermal performance of FPHPs was characterised for different heat input levels; local heat transfer coefficients were estimated by measurement of the heat fluxes and the wall temperatures at different positions in the FPHP. Results showed that the effective thermal conductance of the FPHP was nearly three times higher than that of the material constituting its envelope.