The Gravipod 18” Round umbrella weight bag provides extra protection when weather conditions call for it. Our patented, unique design offers superior durability and performance. Features include: Ballistic Rip-Stop fabric, triple reinforced seams, industrial velcro and an easy-fill top load opening. Our new round weight bag design complements the shape of your round umbrella stand. Simply fill the weight bag with sand, install over the top of the umbrella stand post, and you are ready to go. Filling the weight with sand offers significantly more weight, density, and holding power than water and is not impacted by temperature extremes. The weight will fit over umbrella posts of up to 3.5" diameter. This weight bag holds approximately 0.85 cu/ft or 85 pounds of sand. Please keep this in mind when shopping for sand/ballast. Sand not included with purchase of the weight bag.