3D Systems (DDD), a leading provider of 3D printing centric design-to-manufacturing solutions, has given investors mind-blowing returns over the past few years. From a low of $1.30 in 2009, the shares rose to a high of $97.30 in the beginning of this year. The company has seen staggering revenue growth over the past few years, and net profit has grown at an even more rapid rate. However, since reaching that apex, the shares have declined precipitously.

3D Systems has also taken the lead in the retail-consumer market for 3D printers, which are becoming popular with hobbyists and entrepreneurs. It has recently come out with the Cube 3, a sub-$1000 3D printer aimed at empowering the retail consumer, allowing them to create their own customized product at a far lower cost than in the past. The CubePro, meanwhile, in the sub-$5,000 range, will allow consumers to print much larger items and connects to a broad array of electronic devices. For the first time, such machines are selling through mainstream retail channels such as Staples (SPLS) and Amazon.com (AMZN).

What really has the markets buzzing, however, is the potential for 3D printing to revolutionize manufacturing. Ever since the development of conveyor belt assembly lines about a hundred years ago, industrial-scale manufacturing has been associated with the production of large quantities of standardized products. 3D printing has the potential to change that assumption due to its ability to produce highly customized products with great speed. 3D Systems has announced plans to build a continuous, high-speed fab-grade printer, ramping up the speed of 3D printing. It is doing this by varying from the traditional method of using a mobile print-head that creates layers on a stationary print bed, and moving to a model that makes the print bed mobile and the print head stationary, using an assembly-line model for production. The company aims to become a leader in high-speed custom manufacturing, and has even announced a partnership with Google (GOOG) to help it produce more-customized smartphone designs. 3D Systems also plans to expand capacity and invest in new technologies in the hopes of doubling its revenues over the next few years, and its recent track record gives us optimism on this front.

Stratasys (SSYS), another provider of additive manufacturing solutions, has eight brands, ranging from entry-level 3D printers for hobbyists to large production systems for direct digital manufacturing. The company, which merged with Objet, an Israeli manufacturer of 3D printers, in 2012, expects to see strong revenue growth this year, with organic sales set to grow at least 25%, and further growth coming from the addition of MakerBot Industries, which was acquired last year.

Shares of Stratasys, like those of 3D Systems, have dropped in recent months after rising dramatically over the last few years. The decline is partly due to the expectation of rising operating expenses, as the company is very much in an expansion stage. Stratasys expects to make costly investments in research and development for technology and new products, as well as sales and marketing programs to drive future market adoption.

The long-term outlook for shares of both 3D Systems and Stratasys is unexciting at this time. While the potential for 3D printing to change the face of manufacturing in the future is impressive, the early entrants into the field of new technologies do not always reap the profits as they become widely adopted. Furthermore, while it is understandable that some investors are willing to buy shares at valuations that far exceed the Value Line median for all stocks, the shares are trading at staggering premiums by any valuation metric.

At the time of this article’s writing, the author did not have positions in any of the companies mentioned.