The two most common types of touchscreens are resistive and capacitive. Resistive touchscreens are made up of two layers. When a user touches the top layer, the two layers press together, triggering a touch event. Capacitive touchscreens are coated with a material that stores electrical charge. When a user touches the screen or in some cases even hovers over the screen) with a fingertip or stylus that can conduct electricity, a portion of the charge is transferred to the user, decreasing the panel’s capacitive layer and thus triggering a touch event.
What does this practically mean for interaction designers? Simply this: because of how resistive touchscreens work, they require pressure, but multitouch does not work very well (if at all). Most resistive touchscreens are single-finger only, so you are limited in your palette to gestures that do not require multiple fingers: tap, tap and hold, slide, and drag. (Granted, this is 80% of what users use on any touchscreen.) More subtle gestures, such as flicks, don’t work as well simply because the resistive screen requires pressure. Too little pressure and the system won’t detect a touch event occurring. Sliders, for instance, might not work as smoothly on a resistive screen. A capacitive touchscreen is, in general, more responsive and allows for multiple finger gestures, like pinching, two-finger scrolling, etc. Some capacitive touchscreens even allow for hover states.
Another minus for resistive touchscreens is if the top layer isn’t glass or other hard material, it can wear out over time. Commonly pressed areas can wear out and become difficult to trigger a press event.
Why then ever use a resistive touchscreen? Several reasons. Resistive touchscreens don’t require glass, so they don’t break as often, and can be used in places such as bars, restaurants, and backs of taxis where they will get some punishing use. Most touchscreens that are outside will be resistive, if only for the simple reason that they can be used while wearing gloves in cold weather, because they don’t need to conduct electricity from a finger to make them work. And, bottom line, resistive touchscreens are cheaper. Especially at larger sizes, the savings for a resistive touchscreen can be substantial.
To sum up, if you have a choice, use a capacitive touchscreen if you need to make use of multitouch gestures, if your touchscreen is small (or money is no object), and if your device/installation will be used mostly indoors. If you can afford it, a capacitive touchscreen (for its responsiveness) is almost always preferred, but there are certainly reasons to use a resistive screen. Just be careful with subtle actions on a resistive screen: for instance, use arrow buttons instead of sliders and try not to rely on actions such as drag and drop. Users expect the responsiveness of a capacitive screen, which is why using the touchscreens on the back of airplane seats is such a frustrating experience. With resistive touchscreens, keep it simple.