gravipod 18" square umbrella base weight bag - up to 110 lbs. gravipod our all new and improved patented design offers even better durability - with stronger seams, rugged ballistic rip-stop polyester, and our new extra large easy-fill system featuring a top load opening that makes filling and using your premier tents umbrella weight bag even easier. we took our already terrific design and made it even better. our premier tents umbrella weight bag provides extra protection when conditions call for it. simply fill the weight bag with sand, and you're ready to go. will fit over umbrella posts of up to 3.5" diameter. *sand not included note: this weight bag holds approximately 1.1 cu/ft. please keep this in mind when shopping for sand/ballast. sand not included.