Application Shell Architecture provides an initial static frame, a layout or architecture into which content can be loaded progressively as well as dynamically, allowing users to engage with the Progressive Web Application despite varying degrees of Web connectivity. Technically, the shell is an Application stored locally in the browser cache of the Mobile Device or User-agent.
Application Shell Architecture separates the core application infrastructure and User Interface from the data. All of the User Interface and infrastructure is cached locally using a Service Worker so that on subsequent loads, the Progressive Web Application only needs to retrieve the necessary data, instead of having to load everything.