Velvet garments made from cotton or polyester will not be damaged by water, but get caught in the rain with rayon or acetate velvet and the nap will be permanently disrupted where the raindrops hit.
Touching up Velvet
If you are tempted to touch up a velvet dress with an iron, use steam only as direct contact with the iron will cause permanent damage. Also, when ironing any fabric, check the care label for heat instructions. If a high heat iron is used for a low heat item, the fabric will be damaged. If there are no care instructions, use a press cloth between the iron and the item to protect the fabric.