What happened

Shares of Proto Labs (NYSE:PRLB), a quick-turn contract manufacturer with a growing 3D printing business, jumped 11.8% in September, according to data from S&P Global Market Intelligence.

For some context, the S&P 500 returned 2.1% in the month, while shares of the two largest publicly traded 3D printing players, 3D Systems and Stratasys, rose 3.7% and 5.5%, respectively. 

Proto Labs stock is having a great year -- it's gained 56.8% so far in 2017, through Oct. 5, versus the S&P 500's 15.8% return.

Close-up of 3D printer printing a fuschia-colored plastic object.

Image source: Getty Images.

So what

No notable news about or from Proto Labs came out in September or soon before the month started, to my knowledge. So it's likely we can attribute Proto Labs stock's performance last month simply as a continuation of its robust performance all year, driven by its solid quarterly earnings reports.

On July 27, Proto Labs reported its second-quarter year-over-year revenue increased 9.4% -- or 12.8% adjusted for discontinued services and the impact of foreign currency -- and adjusted earnings per share rose 8.9%. Both headline numbers slightly beat Wall Street analysts' estimates, with the market reacting favorably, driving the stock up to a closing gain of 3.5% on earnings day. 

While its relevance to Proto Labs stock's September performance is debatable, it's worth noting that in early August, Proto Labs announced that it added HP Inc.'s Multi Jet Fusion 3D printing technology to its 3D printing service offerings.

Now what

The pop in Proto Labs stock last month is no reason for investors to change whatever course they've chosen. Investors will be getting material news soon, as the company is slated to report its third-quarter 2017 results before the market opens on Thursday, Oct. 26. 

Beth McKenna has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Proto Labs. The Motley Fool recommends 3D Systems and Stratasys. The Motley Fool has a disclosure policy.