Things You'll Need:
- Square of cardboard Tape measure Utility knife Balloons Helium tank Garbage bags Weights Fishing line Scissors Chairs
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Step 1
Lay a square of cardboard on a flat cutting surface. Draw a circle on the center of the cardboard that is 8 inches in diameter and cut it out with the utility knife. The hole will serve as a sizing guide for the balloons as they're blown up.
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Step 2
Calculate the length of the balloon arch using one of several equations. If the balloon arch will be wider than it is tall, add the height and width to get the length of the arch in feet. If the balloon arch will be taller than it is wide, multiply the height by 2 and add the width to get the arch's length. If the arch's width and height will be equal, multiply the height by 1-1/2, then add the width to get the length.
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Step 3
Determine the number of balloons the arch will require. The balloons will be attached to the arch in clusters of four, and each cluster will add 8 inches of length to the arch. Multiply the length of the arch by 12 to convert the total length to inches. Then divide that number by 8 to get the number of 8-inch segments required to make the arch. Round this number up if it's a fraction. Multiply that number by 4; this is the number of balloons required. For example, an arch that is 12 feet tall and 8 feet wide would require 192 inflated balloons.
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Step 4
Inflate the balloons with the helium tank, sorting them by color into large trash bags that are anchored by weights. Before knotting each balloon, check it against the cardboard size guide. The balloon should be able to slide about halfway into the hole, with the guide fitting snugly around the roundest section.
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Step 5
Tie the balloons together by their knotted tails in pairs of the same color.
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Step 6
Take two different-colored pairs of balloons and twist them together where the tails are joined. Create a cluster of four that has a checkerboard pattern, with like colors diagonal from each other. Continue to make clusters of four in the same manner until all of the balloons are used.
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Step 7
Measure out a length of fishing line that is equal to the length of the arch, plus about 4 feet. The extra fishing line will serve as two 2-foot tails on either end of the arch. Stretch the fishing line taut over the backs of two chairs, suspending it in the air and securing the 2-foot tails with weights.
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Step 8
Rest the first balloon cluster on top of the taut fishing line. Twist the balloons around the line and slide the cluster to the weight on one end. Repeat with a second cluster, situating that cluster on the line so that all of the colors are shifted over one position from the previous cluster. Continue rotating the balloon clusters in this fashion until all of the clusters are fed onto the balloon arch. Rotating the clusters produces the spiral pattern.
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Step 9
Set up the balloon arch. With a partner's help, tie the ends of the balloon arch to handrails, weights or other anchors that are spaced the necessary distance apart.
