Interactive format which allows the mobile ad unit to expand from a traditional size to a larger size.
Expandable banner ad is a quite rare type of ad which opens up when the user interacts with it. The viewer might need to take a certain step, for example click on it, or it can expand automatically. IAB specializes the dimensions of an expandable ad which are characterized as before and after. You should also take into account the direction of ad expansion based on where it is used. Expandable banner usually covers the material on the website making a user pay attention to the ad. They can be very effective as a tool to overcome banner blindness and actually make the website visitors look at the ad and maybe even click on it for further information.
Despite its high effectiveness those ads might be annoying and disruptive if they are constantly interacting with consumers’ website using experience and may result in lower conversion. Thus, you need to be careful when choosing a platform for your ad and deciding whether to use or not to use the expandable banner.