Rapid prototyping is a group of technologies that fabricate physical objects directly from CAD data through additive layer-by-layer processes, unlike traditional subtractive methods like milling. It is also known as freeform fabrication, layered manufacturing, and automated fabrication. While additive fabrication seems new, the underlying technology dates back to the 18th century. Rapid prototyping can reduce design cycle time from weeks to months but still may require many hours to produce an object. It has been used to fabricate objects from materials including liquids, powders, thermoplastics, and gases.