Real or faux silk, taffeta, velvet, brocade or heavy-weight satin (casa satin) would be a good choice.
A prince or princess should be dressed in elegant fabrics that don’t look too plain. Real or faux silk, taffeta, velvet, brocade or heavy-weight satin (casa satin) would be a good choice. Beware of cheap, shiny materials like crushed velvet and halloween-quality satin.