Impression devices are provided for making an impression of a desired feature. The impression devices include: a flexible bladder having a cavity formed therein, the flexible bladder being capable of conforming to the details of the desired feature; a rheological material, such as a magnetorheological fluid, disposed in the cavity of the flexible bladder; and an activator for applying an external stimulus to the rheological material to change the state of the rheological material and thereby capture an impression of the desired feature.