The 3-D printing industry has been on an absolute tear over the past year, with several initial public offerings and numerous all-time highs for companies in the industry. The most spectacular example of optimism in the industry can be found in voxeljet's (NYSE:VJET) recent IPO. This 3-D printer company's shares rose more than 100% after its IPO. So just how do investors in this hot sector determine which companies are the most expensive to invest in?

When we look at the crop of publicly traded companies -- which include 3D Systems (NYSE:DDD), Stratasys (NASDAQ:SSYS), Arcam (NASDAQOTH:AMAVF), ExOne (NASDAQ:XONE), and voxeljet -- it can be very difficult for average investors to determine just how much they are paying for these companies. At first glance, it appears voxeljet is more than twice as expensive as its competitors, but given its growth rate, is it still the most expensive? 

* Profit and revenue yields assume five-year CAGR equal to two-year rate and gross margins of ~55.6%.TTM is equal to 12-trailing-months sales. CAGR is equal to compound annual growth rate.

In the video below, Motley Fool analyst Blake Bos looks into the valuation of all of the 3-D printing companies mentioned above, gives his take on the least and most expensive, and teaches investors a valuable way to quickly evaluate growth stocks. If you have any questions, be sure to ask below or tweet Blake through Twitter here.