Paper or wireframe prototypes tested early in the design process can identify numerous design issues. This type of low-fidelity usability testing is cost-effective, fast, and easy, and helps explore metaphors and conceptual models along with navigational structures and flow patterns. Usability issues are identified and designs can be iterated and refined for further feedback and testing.
High-fidelity prototypes can be built in HTML or applications such as Microsoft Visio, Silverlight, or Adobe Flash to test a more realistic or immersive interactive experience. This is useful when most or all design work is done up-front so that final candidate designs can be tested and refined before a development hand-off.