Ammonia sensing and detection are of contin-ued arising interest for a wide range of applica-tions, such as medical, environmental, chemi-cal, food industry, etc. Among the options to implement as the active layer in ammonia sen-sors, the organic polymer-based, polyaniline (PAni), has been largely investigated due to many advantageous properties highlighting the facile-preparation and cost-effectiveness. A matrix can be incorporated into this polymer, since making conducting polymer composites may enhance some device features when com-pared to the pristine conducting polymer. Here-in, we have developed chemoresistor-based sensors by mixing polyurethane (PU) to PAni in different weight ratios. For that, we have casted solutions from this mixture onto gold interdigitated electrodes on a kapton polyimide flexible substrate. Analyzing the outcome, we could observe that the proportion between the polymers affected directly the sensor's response, especially when compared to the pristine PAni sensor. The sensing profile demonstrates that is yet the de-doping of PAni by the NH3 the main responsible for the detection. Anyhow, from optical and morphological measurements, the presence of PU is responsible for improving the structure and conformation of the devices, without interfering with the PAni chemical nature. From our results, we obtained sensitiv-ities up to 0.4 %/ppb and a limit of detection of 5 ppm. Moreover, the presence of PU protects the sensor from the influence of the relative humidity (RH) variation, which can be seen through the higher difference in the relative responses of the mixed and pure PAni devices (Fig. 1). This hydrophobic nature due to the PU addition was also observed by wettability exper-iments. Such a characteristic allows a more precise measurement of the ammonia concen-tration in environments where the RH is not constant, which is essential for most industrial applications.