Stratasys 3D Printing: Discovering Your 3D Printer’s Capabilities
Some designs can be ‘self-supporting’ and not require a support system. This ‘self-supporting’ design is dependent on three variables; technology, material and layer thickness. For example, because Polyjet is printing drops in micron layers every down-facing surface must be supported, otherwise gravity will cause it to fall. But other technologies such as FDM (Fused Deposition Modeling) can have enough strength to build a layer that slightly overhangs the previous layer to produce an angle.
Source- Computer Aided Technology Blog.