As the sensor is flexed, the resistance across the sensor increases. Patented technology by Spectra Symbol – they claim these sensors were used in the original Nintendo Power Glove.
The resistance of the flex sensor changes when the metal pads are on the outside of the bend (text on inside of bend).
Note: Please refrain from flexing or straining this sensor at the base. The usable range of the sensor can be flexed without a problem, but care should be taken to minimize flexing outside of the usable range. For best results, securely mount the base and bottom portion and only allow the actual flex sensor to flex.