Crystal is very dressy for both formal and informal nights. Lots of long gowns, sparkly dinner suits ( think Chanel or St. John---you don't need to wear that line, but it gives you an idea of the look), evening pants and sparkly tops for the women and a tux or dinner jacket for the men (98% wear tuxes). Informal means a dinner suit or dressier dress for the women and a jacket, dress shirt and dress slacks for the men.