From Flux Developer Wiki

Cylinder

The Cylinder node is as one might expect. You can specify the Height and Radius of the cylinder. The cylinder is aligned along the local y axis. When the Cylinder Property Page is active, you can change the size parameters by dragging the mouse on the screen. The coordinate that is closest to the movement of the mouse will get modified.

If the Solid toggle is ON, then the backfaces are not rendered ( because it is assumed that the shape is solid, thus you can't see inside it, so you don't need to draw backfaces ).