The marbles in this Sunset series are all hollow. They are a thicker walled hollow, so they are not as heavy as your typical boro marble, and not as light as a thin walled hollow - a nice feel in your hand. WOW - those colors!!! This is one of the most beautiful marbles I've seen color wise, really fantastic. It is just flat out elegant and gorgeous, with the pinwheeling floating up above the color.