Decorative Novelty's Vacuum Formed Boulder is made from heavy gauge plastic, suitable for indoor or outdoor use. The boulder is hollow for storage. Decorative Novelty's Rock Set x 3 is made of natural Fiberglass. The rock Set nests into each other for easy shipping & storage. Rocks can be used indoors or outdoors.   The Boulder Sizes are: Boulders:21”h x 31”l x 26’w   The Rock Set x 3 Sizes are: (all 3 sizes per set) Small Rock Size: 13"l x 12"w x 6"h Medium Rock Size: 16"l x 14"w x 7"h Large Rock Size: 20"l x 15"w x 8"h       Boulders   Rock Set x 3