Run & Fly Retro Paisley Short Sleeve Printed Slim Fit Short Sleeved Rayon shirt made with a bit of stretch 
The approximate sizing is as follows:
S – 36″ – 38″
M – 38″ – 40″
L – 40″ – 42″
XL – 42″ – 44″
2XL – 44″ – 46
3XL - 46 - 48