These lightweight mesh jerseys first appeared in the late 1970's and were worn during Spring training and pre-game warm ups. By the mid 1980's, most teams had adopted the standard of the mesh BP as their practice jerseys. Mitchell & Ness not only ensures that every jersey is 100% authentic, but also captures the spirit of the era in which it was originally worn. Made of 100% polyester soft, textured, lightweight mesh. Team graphics made to the specifications of the original jersey. Officially licensed by Major League Baseball. Size scale is as follows: M = 40, L = 44, XL = 48, XXL = 52.