Hi Dixieland Dancer!

They use a digital transfer printing process on clothing products. Here's a description from their website:

Digital transfers are printed on our high speed digital printing press. They are as durable as screen printing, but offer more detail. Digital transfers use heat to create a bond between the resin and the t-shirt locking the ink between the two layers. Digital transfers have a slight plastic feel when first worn, however, this feel will diminish after washing.
The t-shirts I've gotten from them have all looked incredible. Whenever I've done the iron transfers from home though, they haven't looked so good. The colors are always faded. The bright detail is lost, whereas I haven't had that experience with Cafepress.

Edited to add: The quality is based on having a high resolution graphic though. If you don't have the right dimensions then it's not going to look good.

Par...