Using a Forming Tube (also called Sonnet Tube) creates smooth-walled columns underground. This is important so that when the ground freezes, its icy mass can't grip the walls of the footing and heave it about. Most cities require the use of forming tubes, or at least a good substitute strategy such as rolling up old linoleum or tar paper and making your own.

The excess cardboard around the outside peels away like an orange skin. The bolt in the middle is used for attaching the post bottom hardware.