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. This is probably my personal favorite of this bunch. I just love the dot and pinwheel work, and I love how you can see the shadows of the dots and such on the color below. The layers of glass goodness are just awesome in this one!!