Foil balloons are made using plastic sheets that have been metallised. The very first foil balloons were created by NASA for space missions. They used Mylar for their balloons. You can create your own foil balloons at home using thermoplastic foils. Nylon and polythene foils are thermoplastic. These foils can be sealed together using heat. The heat melts the plastic and then, upon cooling, the material solidifies into one layer instead of two. Avoid foils that are made of thermosetting materials as heat cannot melt them so you cannot create seams.
Cover the table with two layers of craft paper. This will protect the table from any damage.
Trace the balloon on a piece of paper. You can draw any shape that you want. Because balloons are three dimensional, the pattern needs to be larger than the actual balloon. To determine the actual size you must be aware that when the balloon is inflated, its circumference is half the circumference of the pattern. Therefore, the pattern must be 50% larger than the actual balloon.
Choose a spot on the pattern for the filling point. This will be a neck that is one inch wide by four inches long. Cut out the pattern using a pair of scissors.
Roll the foil out on the table with the nylon side facing up. Tape one edge down, stretch the foil and then tape the other edges. When taped, the foil needs to be free of wrinkles. Tape another sheet of foil on top of the first piece. This time the nylon side is facing down. Tape the edges and ensure the foil is wrinkle free.
Place the pattern on top of the foil and trace around the pattern using a permanent marker.
Plug in the heating iron and test for good sealing heat. The temperature will be different for all irons. Use scraps of foil to test the heat. Press the hot iron onto a small piece of foil folded over. Let the foil cool and attempt to peel the seam apart. The temperature of the iron is too hot if the seam is crisp or melts. If the iron is not hot enough, the seam will peel apart.
Seal the balloon once you have found the proper temperature. Place a piece of waxed paper over the outline. Press the hot iron around the outside edge of the outline. Start ironing on one side of the filler neck and work your way around to the other side of the filler neck. Do not seal over the filler neck otherwise you cannot inflate the balloon. The waxed paper makes ironing easier and creates nicer looking seams. Once you are done, place the iron on the floor but do not unplug or let it cool down.
Plug in the hot knife and let it heat up. You want a higher temperature than the iron in order to cut the foil. Test the heat with scraps of foil. The knife needs to be hot enough so that its cuts the foil by melting it.
Cut out the balloon using the hot knife. Cut along the outside edge of the seam, leaving about half an inch of seam on the balloon. Move the knife slowly and make sure you are cutting through both pieces of foil. Avoid chop marks by curving over any areas where the direction changes. Chop marks tend to tear easily.
Peel the balloon up off the table. Go slowly to avoid tearing. Remove the leftover foil from the table and place the balloon back onto the table upside down.
Check the back side seams. If they are blistered, gathered or not sealed then re-iron the seams as in step 7.
Inflate the balloon with helium or air. Inflate slowly as over inflation or rapid inflation can peal the seams or tear the balloon.
Quickly seal the filler neck with the hot iron once the balloon is inflated.
Unplug the iron and knife and clean up your work area.