Plastisol is the standard ink used in screen printing.
Before plastisol ink made its way into screen printing in the 1970’s, printers primarily used water based ink. Plastisol ink has it’s advantages.
Water based inks have improved since the 1970’s, but what made plastisol ink popular was that it gave printers the ability to create vibrant prints that stand up on top of the garment. Many water based inks are fine for printing on light color fabrics, but you don’t always get the burst of color you can with plastisol ink due to the fact that they settle down into the fibers. A primary complaint against plastisol inks is that they are thicker than water based and more difficult to push with a squeegee. However, you can thin plastisol ink by adding a reducer. Caution, though, too much reducer can not only thin the ink but affect its opacity. As a result, it will not appear as vibrant on darker garments.
Another advantage is that you can leave plastisol ink in your screens. Unlike water based ink, it does not dry if left out.