BE AWARE that the non-returnable balloon gas containers sold on the internet and in some chainstores often quote the very much smaller 9” (23cm) balloon for number filled and that some supply a balloon air mixture that give a lower flying time. A 9” (23cm) balloon is HALF the volume of the standard 11” (28cm) balloon. See chart below. RETURNABLE GAS BOTTLE SIZES Inflation cost (per balloon) reduces as purchase gas volume increases. You can buy even better if you buy a "Party Pack" comprising gas, balloons and clipped ribbons in matching colours. All gas bottles are supplied with a regulated "tilt " valve that makes inflation child's play. Simply fit the neck of the balloon over the rubber Tilt Valve nozzle and tilt the nozzle sideways. When the balloon is fully inflated - release the valve. DO NOT over inflate your balloons or you will run out of gas. You may remember from school that the volume of a sphere goes up as the cube of the radius. Small change in diameter - big change in volume!