Taller half-mil bags also work, but are hard to find. Sometimes hobbyists tape two dry cleaner bags together to make a larger bag. In warm weather, dry cleaner bag balloons tend to hover at first, with very little net lift. At high elevations, dry cleaner bag balloons may not fly at all. Welds are made with a heated pizza cutter , on top of a wooden board.
Scotch tape repairs any weak spots.
To stabilize the balloons, the bags are tapered, and small ventilation holes are made. Engines are made by melting birthday candles together with a heated fork . Alternately, dripped wax can melt the candles together. The most efficient engines are single-file . They get maximum oxygen and cooling area.