Sand Bag for Feather Flag Bases Sand Bag for Feather and Teardrop Flying Banners. Heavy-duty nylon Sand Bag measures 18x19 inches and holds up to 30 lbs of sand. Its reinforced Velcro closure ensures durability and easy reusability. This sand bag has a reinforced opening in the center to fit on most flag bases. It is strong enough to secure both indoor and outdoor flagpole bases. For stronger winds, multiple sandbags may be needed to secure the base.