Factories, the chief innovation of the industrial revolution, are cathedrals of productivity, built to shelter specialized processes and enforce the division of labor.

Adam Smith, who illuminated their function on the first page of The Wealth of Nations, offered the celebrated example of a pin factory: “I have a seen a small manufactory… where ten men only were employed, and where some of them consequently performed two or three distinct operations. [They] could make among them upwards of forty-eight thousand pins a day… Separately and independently… they certainly could not each of them have made twenty, perhaps not one pin a day.”

But the benefits of factories suggest their limitations. They are not reprogrammable: To make different products, a factory must retool with different machines. Thus, the first product shipped is much more expensive than the next million, and innovation is hobbled by the need for capital expenditure and is never rapid. More, specialization compels multinational businesses to circle the globe with supply chains and warehouses, because goods must be shipped and stored.

Jason Pontin (@jason_pontin) is an Ideas contributor for WIRED. He was formerly the editor in chief and publisher of MIT Technology Review; before that he was the editor of Red Herring. Now he is a senior partner at Flagship Pioneering, a firm in Boston that funds companies that solve problems in health, food, and sustainability. Pontin does not write about Flagship’s portfolio companies nor about their competitors.

All that is about to change. In another industrial revolution, humans are making new things in novel ways into hitherto impossible shapes, using the technology of a fizzled craze: 3-D printing. This summer, I visited the future of manufacturing at the headquarters of Desktop Metal, a startup in Burlington, Massachusetts, which is building printers that make metal parts. Co-founded in 2016 by the serial entrepreneur Ric Fulop and four MIT professors, including Emmanuel Sachs (who first coined the term “3-D printing”), Desktop Metal has raised over $277 million from investors such as Kleiner Perkins, General Electric, BMW, and Ford, and is valued at more than $1 billion. (Disclosure: I have known Fulop, best known for starting the failed battery company A123 Systems, for more than a decade.)

To grasp why Desktop Metal’s machines are so important, it’s necessary to understand “the 3-D printing revolution that wasn’t.” For all the froth surrounding the idea of 3-D printing half a decade ago, actual 3-D printers were disappointing: most consumers didn’t want the things that 3-D printers made, and manufacturers wanted things that 3-D printers couldn’t make at all.

Hobbyists and members of the maker movement use desktop 3-D printers, typically costing a few thousand dollars, to print plastic parts from digital designs. Machines like MakerBot’s Replicators heat polymers and squirt the material out of a printer nozzle; but 3-D printed polymers are mostly good for prototypes, because they look rough, unfinished, cheap. On the other hand, advanced manufacturers like GE manage huge printers, which can cost more than a million dollars, to make a limited number of high-value parts. Their “additive manufacturing” machines use lasers or electron beams to fuse metal powders into complicated shapes; but while the process can fabricate the nozzles of a $35 million jet engine, it’s slow, expensive, and dangerous. (Typically, additive manufacturing machines must melt powders in a vacuum because the fusing metal would explode if combined with oxygen.)

3-D printing could transform manufacturing. But almost everything that businesses make—from phone cases to propellers to drills—lies between these bookends of tchotchkes and jet-engines, and is often made of metal or composites of metals and other materials. Desktop Metal wants to serve that fat middle market of metal fabrication, worth more than a trillion dollars. Fulop, the company’s CEO, says, “During first 20 years of 3-D printing, the technology was too slow and expensive, so its primary use was prototyping. Today, 3-D printing is finally starting to be used for high-volume, mass production.” The cohort of 3-D plastic printing and additive manufacturing businesses is swelling, but right now Desktop Metal is the only company focusing on 3-D metal printing, and its valuation reflects the intellectual property they own.