Hi Ama,When weight is reerfed to, most of the time it has to do with the thickness of the thread and what tension it will break under. Ultra, I am assuming without seeing or feeling the shirt refers to the finnesss of the cotton. Usually a treatment and thread count. By the short discription I am guessing that it means thread count and treatment of fabric or how it was produced. Probably in reference to chemicals, cold or hot water applications and or stabilizing agents. Hope that helps.