An interstitial creative is an ad that either floats on top of a publisher's page on desktop or fills the screen on a mobile device. It's also known as a floating or prestitial ad. This ad format allows flexibility. Because it isn't assigned to a fixed ad slot, it can be almost any shape or size, and you can place it anywhere over a publisher's content.
This guide walks you through the process of building an interstitial creative using the Studio HTML5 SDK. After you've built the creative, you can serve it in both desktop and mobile web formats.