Whilst ribbed tshirts aka ‘tshirts with lines’ have a great stretch and fit for most people, there is a post-printing issue and it’s best to stay away from screenprinting or using flex or flock on those type tshirts.
A screen printed or heatpressed flex/flock image will rest on top of the ribbed lines; and when tshirt is worn, the fabric will stretch exposing areas in between the ribs where the ink didnt get to in the case of screenprinting or unsightly stretched out look in the case of flex/flock prints.
Our advise if there are no other tshirt options is to use one size bigger tshirts for your order. In that case the print-gap issues would not be as bad.
Material Credit: http://www.threadbird.com