Help please .

I really need the answer to next question .I was puzzled by this translation .How to ask in English ,is this correct? :What is the stuff/material is this T-shirt made of? (For example the situation in a clothes store :I'm looking for a T-shirt and I wonder about the material of this T-shirt (Cotton ,nylon ,silk ,etc.) and I want to have this question answered by shop-assistant) .I'll be really glad to receive an answer .Thank you in advance .