gravipod 18" round umbrella base weight bag - up to 85 lbs. gravipod our latest design features new heavy duty materials - ballistic rip-stop polyester with triple stitch locked seams. gravipod umbrella base weight bags are rugged and dependable, and will provide that critical extra protection when conditions call for it. simply fill the weight bag with sand, install over the top of the umbrella stand post, and you are ready to go. will fit over umbrella posts of up to 3.5" diameter. our new round weight bag design complements the shape of your round umbrella stand, all while adding the extra weight needed to keep your umbrella where it should be. see our website for video instructions on the filling and use of your new gravipod round umbrella weight bag. note: *sand and umbrella stand not included, product volume is approximately 0.85 cu/ft, please keep this in mind when shopping for sand.