When investors talk about 3-D printing being the next "trillion-dollar revolution" they're referring to the addressable manufacturing market that 3-D printing has the potential to replace. In a recent interview, the CEO of Materialise, who was recently voted the most influential person within the 3-D printing industry, believes that 3-D printing has the potential to represent up to 30% of the worldwide manufacturing industry. In 2010 terms, this would make 3-D printing a $3 trillion worldwide industry. With the 3-D printing industry only worth a few billion dollars today, not only does this proclamation seem farfetched, it seems downright impossible. In this video, Motley Fool contributor Steve Heller discusses whether this is even possible, what sort of time frame is under consideration, and offers his favorite 3-D printing investment today.