It is 50% polyester, 37.5 % heirloomed combed and ring spun cotton, 12.5% rayon. 

278 grams per square meter.

FOR REFERENCE: I have one that is size small (Sarah normally wears an XS or Small) and I washed it on cold and lined-dried and it did not shrink. If you run on a hot load and dry it probably will shrink.