depends on which way the material is cut to make the t shirt.
I am not on commission, and the postage is hefty, but these t-shirts are fab - slightly shrink all over first wash or tow but hold their shape and last forever.
http://www.egyptiancottontshirts.com/
In the process of making paper... almost anykinf of paper, the 'weave' or grain, if you will runs only in one direction. In fact it has a term, called "warp and woof"... (you'll notice paper tears easily and rather straight in one direction but not the other)... same holds true with many fabrics...