You can preload (from the app only) available sessions in advance, ideally using a Wi-Fi network to avoid data charges. You can then play them when in airplane mode or when you have no internet connection.
To do this, tap on the little cloud icon near the session name to preload it.
When the session has preloaded, the icon changes to a smartphone symbol.
This allows you to play sessions on your phone wherever you are, even if your phone has no signal (indoors or in a basement space, for example) or if the signal isn't very good (on a bus or underground train). You can even choose to deliberately switch off the mobile or Wi-Fi network to avoid being disturbed.
To play preloaded sessions:
Simply keep the app open and tap the Play button.
Smartphone and tablet media readers can't play the sessions as they have been encrypted to prevent illegal copying.
To delete preloaded sessions:
Click on Downloads and Delete All at the bottom of the page.