Plastisol Inks can be printed on just about any textile that can withstand the heat required to cure the printed area. Plastisol Inks do not color garment fibers like a dye or water based inks. Rather the ink wraps around and sits on the surface of the fibers bonding with the fabric.
Plastisol prints are by far unmatchable in it's printing properties and characteristics. Alternative Printing methods like "Direct to Shirt",(used by zazzle.com), or Heat Transfer Graphics, (used by cafepress.com) have attempted to make custom t-shirts on demand, however cannot be compared to an actual printed T-shirt with Plastisol Inks. These alternative methods are far inferior in aspects of color brilliance, texture, durability, and economical value. Plastisol Prints will often out last the actual shirt that its printed on.
These inks are extremely verastile in that they can be printed on both light and dark garments. However there are a few variables to consider, if you plan to print a single design on multiple garment colors.