Things You'll Need
If you're throwing a party and think you'll be needing a large number of helium balloons, having them filled at your local party supply store could get expensive. Transporting helium balloons is also quite a hassle--you can find yourself batting them away from your face as they fly around the back seat of your car. The cheaper and more convenient option is to rent a helium tank or purchase a disposable helium tank and fill the balloons with helium at your home or at the party's location.
Get the supplies
Rent a helium tank--they're often available at stores that sell party supplies. Most such stores have a variety of tank sizes available, depending on the number of balloons you wish to fill. Note that if you rent a tank, you'll probably have to leave a deposit and be responsible for returning the tank.
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Purchase a disposable helium tank if you'd rather not rent. You can do this at your local party supply store or online. Disposable helium tanks generally fill about 30 to 50 nine-inch latex balloons. As of September 2010, they were priced from $40 to $60.
Purchase balloons and ribbon. The store where you buy or rent the helium tank will most likely have some in stock, or the disposable helium tank may come with some. If you're looking for a wider variety of balloons, your best bet is to visit your local party supply store. They will have standard latex balloons, as well as foil balloons that come in all kinds of shapes and sizes. Either way, choose the color and style of your balloons according to the theme of the party.
Set up the Balloons
Fill the balloons with helium. If you rented a helium tank, a store employee will show you how to use their tank and how to read the helium gauge. If you've purchased a disposable helium tank, it should come with a set of instructions.
Tie the neck of each of the filled balloons into a tight knot. The tighter the knot, the longer the balloon will float.
Cut a strand of ribbon to a desired length. If you're tying several balloons together, it's best to use different lengths of ribbon to give the balloons a layered look.
Attach a strand of ribbon to the balloon by tying it just under the knot of the neck.
Attach the balloon to a weight to keep it from floating away. Tie the ribbon to a standard plastic balloon weight, a table centerpiece, or the back of a chair.