Fabrics like denim and cotton provide the best base for iron on patches. Look at the fabric care label to see whether it can be ironed (if not, there will be a crossed-out icon of an iron). If there's no label, try to figure out what material it's made of. Be very careful with polyester fabrics, since applying the high heat necessary for ironing on patches can burn the fabric or cause it to get discolored. Silk and other delicate fabrics are not good candidates for patches.
