When a ribbed garment is pulled onto the press for screen printing, it is not stretched out. When the ink is applied it will sit on the top of the ribs. When worn the material stretches and the ribs will pull apart exposing a non-printed area in between the ribs.

Is there any way to prevent this from happening?

We can apply more pressure on the press when screen printing on ribbed shirts and garments to try to force the ink into the gaps, but this limits the amount of detail that is actually shown when printing on the ribbed garment. Because of these issues, we strongly suggest that you do not print on ribbed garments.