Flex sensors are relatively helpful in determining how much bent there is on a particular object. For example, you can use flex sensors on a glove to determine how much you bend your fingers.
 
Flex sensors are actually passive resistive devices. When the flex sensor is bent, the resistance of it increases depending on how much you bend it. This could be use to determine how much an object is bent by comparing the initial resistance of the unbent flex sensor to the current bent state. Applications of flex sensors may include determining joint movement in robotics, a virtual reality glove that is used to control certain interface, etc.
Connector is 0.1" spaced and bread board friendly. Check datasheet for full specifications.
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.
Flat Resistance: 25K Ω
Resistance Tolerance: ±30%