Prototypes can be very different depending on their purpose and the time available to create them. There is no limit to the kinds of prototypes you can create. At the end of the day, prototyping is about experimenting. However, here are some common approaches you can get inspired by to create your own approach to prototyping. These different existing approaches are characterized by two key aspects:

• The fidelity level defines how realistic the prototype looks
• The interaction level defines the degree to which the prototype responds to the user actions

Based on the fidelity level, you can find prototypes resembling real products to different extents:

• Paper prototyping is a low-fidelity approach to prototyping. It consists of cutting, combining, and moving around pieces of paper with different parts of the interface on them. You can sketch different screens of your app, show it to a user, and switch from one to another to simulate the interaction the user would have when the user touches the sketch on the paper.

You can use pre-designed templates such as those provided by http://sneakpeekit.com/ to sketch on top the shape of a device or a browser frame, or print different UI widgets such as buttons or checkboxes to combine them. The flexibility of the paper medium allows you to quickly sketch new states in response to user actions that you didn't plan in advance. However, since users will be interacting with sketches on a piece of paper it is much harder for them to feel how using the final product would be.

The low entry barrier of paper can be very convenient for participatory design workshops where you can involve users to express their own ideas. Prototypes created by users may not capture ideas ready to be adopted, but they are useful for designers to learn more about the problems to solve and which aspects users care about in a solution.

• Low-fidelity digital prototypes use a similar idea of connecting multiple sketches to simulate interactions, but they apply the concept to the digital world instead. This allows prototypes to be used in a real device or shared digitally with people around the world. However, users will still be presented with sketches that show an abstracted view of the product.

You can make the sketches on paper and transfer them to a digital format by taking a picture or scanning them, or you can create them digitally. In any case, you will connect the sketches together in a prototyping tool to define how they will react to different user interactions.

• High-fidelity prototypes are realistic enough to be indistinguishable from a real product. Even if these prototypes cut some corners or skip some steps to approximate the intended experience, a user is able to get immersed in that experience. Users will communicate what they experience directly, without any effort of imagination Creating these prototypes requires more advanced tools to produce realistic assets and also combine them in a prototype.

Apart from their fidelity level, another factor that determines the nature of a prototype is their interaction level. Prototypes can provide different levels of interaction, making the user take a more active or passive role.

• Non-interactive prototypes include static images showing how the product would look in a specific context, or videos showing what an interaction would look like. In these prototypes, users do not have the control, which avoids the need for you to prepare the prototype for potential user actions. The audience can comment on what they see or how they react to an idea represented in the prototype. These prototypes are very useful to get reactions from a wider audience, but you will not get feedback based on actual behavior.
• Interactive prototypes allow the user to act on the prototype in the same way they would do with the final product. Users get a more immersive experience and behave in a more natural way compared to noninteractive prototypes. Interactive prototypes make it possible to extract conclusions based on the actual user behavior instead of their initial impressions and opinions.

In this book, we will focus mainly on high-fidelity interactive prototypes since they allow you to get the most valuable feedback. Nevertheless, the techniques you'll learn will be useful in creating any other kind of prototype. For example, once you have created an interactive prototype, you can easily record a video showing a specific workflow to create a noninteractive prototype.