A shiny Mylar balloon designed for use with helium has a self-sealing valve, so there's no balloon-tying involved. While you can use a foil balloon pump to inflate them, if you want them to float in the air, you will need to use helium instead. There may be some variations in how different helium tanks work, so be sure to check the instructions before you get started.
To inflate these balloons properly, fit them onto the nozzle of the helium tank; turn on the tank and slide each balloon off the tank nozzle once it appears fully inflated. Squeeze the self-sealing valve between your fingers to seal the balloon.
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Filling a Mylar Balloon
Step 1: Place Balloon on the Nozzle
Locate the opening on the Mylar balloon. Slide the opening 1 to 2 inches over the nozzle on the helium balloon tank.
Some deluxe or professional helium balloon tanks have separate nozzles for latex and foil balloons. If your tank has two separate nozzles, inspect them both for markings that indicate which is for foil, or visit the manufacturer's website to determine which is which. Inflating a foil balloon with a latex nozzle may damage the balloon.
Step 2: Inflate the Mylar Balloon
Push the nozzle toward the tank while holding the balloon securely in place to begin inflating the balloon. On some models, the nozzle may be pushed down instead of back toward the tank.
Some helium tanks have a separate handle that must be turned counter-clockwise in order to release helium. To use this type of tank, turn the handle counter-clockwise, then place the balloon over the valve and press the valve back or down to inflate the balloon.
Step 3: Seal the Mylar Balloon
Watch the balloon carefully as you inflate it. Slide the balloon off the tank nozzle once it appears nearly full, squeezing the area previously over the nozzle to keep it sealed. The pressure from your fingers seals the self-sealing neck of the balloon.
If you wish to tie a ribbon onto the end of the sealed balloon, tie the ribbon beyond the end of the self-sealing portion of the neck, or else the tied ribbon may loosen the seal and allow air and helium to escape the balloon.
Refilling Mylar Balloons
You don't have to discard a Mylar balloon that has lost most of its helium. Instead, gently push the self-sealing balloon neck back over the nozzle of the helium tank, loosening the seal. If there's a ribbon tied onto the balloon, remove it before attempting to reinflate the balloon. Then, add more helium until the balloon looks nearly full again. Re-seal the balloon and tie the ribbon back in place.
You can even save foil balloons and reuse them. Empty out any remaining helium by placing a straw inside the self-sealing valve until the balloon deflates, and then smooth the balloon flat and fold it for storage.
Do not overinflate the balloon; it will stay inflated longer with slightly less helium inside. Overfilling may cause the self-sealing valve to fail.