Custom design on the front or back of the shirt. Sublimation or Heat Transfer Vinyl dependant on the design.
 
Heather in apparel is when small gray pieces of fabric are woven in with another color. 
 
5.3 oz., 100% preshrunk cotton
Ash Grey is 99% cotton, 1% polyester
Sport Grey is 90% cotton, 10% polyester
Double-needle stitching throughout
Taped shoulder-to-shoulder
Seamless rib at neck
Ribbed cuffs