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Short interest during the two-week period ending January 31 rose on two of four 3D printing stocks we follow. Year-to-date share price gains have been strong for these stocks, ranging between 7.3% and 29.0%. Short sellers have gotten the message and many have apparently decided to wait it out.

Short interest in 3D Systems Corp. (NYSE: DDD) rose by 0.6% to 22.52 million shares. Some 21.2% of the company’s float was short. Days to cover rose from six to eight. In the two-week short interest period, the share price rose by about 5.4%. The stock’s 52-week trading range is $8.31 to $19.76, and shares closed at $17.15 on Thursday, up about 3.8% on the day.

Stratasys Ltd. (NASDAQ: SSYS) saw short interest rise by 2.2% in the final two weeks of January to about 4.81 million shares, or 9.8% of the company’s float. Days to cover rose from five to eight. The share price rose by about 5.4% in the two-week period, and the stock closed at $20.85 on Thursday, up about 5.8% on the day. The 52-week range is $14.48 to $30.46.

Short interest in ExOne Co. (NASDAQ: XONE) slipped by 0.9% to 2.15 million shares. About 19.9% of the company’s shares were short. ExOne’s share price dropped about 5.4% in the two weeks. The stock’s 52-week range is $7.92 to $16.15, and shares closed at $10.02 on Thursday, up 3.1% for the day. Days to cover rose from 14 to 16.

And short interest in Voxeljet A.G. (NYSE: VJET) decreased by 1.6% to 525,727 American depositary shares, with days to cover rising from eight to nine. The share price fell 3.3% in the period. Voxeljet closed at $3.33 on Thursday, up 4.7% for the day, in a 52-week range of $2.82 to $6.50.