Efficient antenna solutions are demanded by variety of applications nowadays. As a part of subterahertz (sub-THz) electronics, they are of use in modern wireless modules and systems, providing opportunities for an ultra-high speed data transfer, remote sensing, energy harvesting, etc. The appearance of robust flexible antennas and metasurfaces can substantially widen the scope of potential application of sub-THz wireless technologies, bringing them to practical use cases. This study focuses on the properties of polyurethane and hydrogel polyurethane films in the context of their spectral characteristics and technological robustness. The thicknesses of the films are 0.18±0.01 mm and 0.15±0.01 mm. Calibrated quartz handlewafers are used to mount them into the optical path of the employed sub-THz reflectometer. At 130–160 GHz, we measure complex permittivities of 2.95 (1 + 0.01i) and 3.15 (1 + 0.01i), making both films well-suited for designs of planar antennas on quartz. Hydrogel polyurethane film, however, does not demonstrate selectivity to acetone-assisted lithographic processes, leaving polyurethane film as the only candidate for cleanroom fabrication.