What causes the ink to fade when laundered?

Again, under-cure can cause ink to wash out, which will give the appearance of a fade, but if this is the case, the wash out is very uneven and splotchy.

Actually, the most common cause of fading is fibrillation. This condition is caused by the shirt fibers pushing through a thin ink deposit during the laundering process, creating an illusion of a fade. In this case, the fade is very even and consistent throughout the design. It is most noticeable with dark color inks on white 100% cotton shirts. Thicker deposits of ink (using lower mesh counts) or a matte clear overprint will reduce the effects of fibrillation.