Using supported ionic-liquid membrane (SILM)-inspired methodologies, we have synthesized, characterized, and developed a humidity sensor by coating a liquid composite material on a hygroscopic and porous substrate. Similar to pH paper, the sensor responds to the environment's relative humidity and changes color accordingly. The humidity indicator is prepared by casting few microliters of low toxicity reagents on a non-toxic substrate. The sensing material is a newly synthesized liquid composite, which comprises a hygroscopic medium for environmental humidity capture, and a color indicator, which translates the humidity level into a distinct color change. Sodium borohydride was used to form a liquid composite medium and DenimBlu30 dye was used as a redox indicator. The liquid composite medium provides a hygroscopic response to relative humidity, and DenimBlu30 translates the chemical changes into a visual change from a yellow to blue color. The borate-redox dye based humidity sensor was prepared, then Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, and image analysis methods were used to characterize chemical composition, optimize synthesis, and gain insight into sensor reactivity. Test results indicated that this new sensing material can detect relative humidity in the range of 5-100% in an irreversible manner with good reproducibility and high accuracy. The sensor is a low cost, highly sensitive, and easy-to-use humidity indicator. More importantly, it can be easily packaged with products to monitor humidity levels in pharmaceutical and food packaging.