If you are familiar with foil balloons you will be aware that the gas (helium or air) is blown into the balloon via a valve in the tail of the balloon usual using a suitable adaptor which is a relatively easy task, without an adaptor it is a little more problematic.

Small foil balloons are manufactured with a valve up inside the tail at the bottom of the balloon. The valve has to be opened to inflate or deflate the balloon. The valve is a few inches up the stem of the balloon which makes it hard to blow up the balloon by mouth. To open the valve gently push a drinking straw up the stem until you feel resistance, that's the valve. Push slightly passed the valve to establish an airway. Use your fingers to seal the balloon around the straw. You can then inflate the balloon by blowing into the end of the straw. If you have a hand operated balloon air pump, a bicycle pump or a foot pump you don't need to use a straw. Just insert the nozzle into the stem and again seal the balloon around it with your fingers. The pressure from an air pump will automatically open the valve as you inflate it.

Foil balloons are fully inflated when most of the wrinkles are gone--they don't expand like latex balloons and will pop if overinflated; wrinkles therefore are to be expected. Similarly remember foil balloons are different to latex balloons in that once the basic shape is achieved you can’t make the balloon bigger by the addition of more air; it will burst if over inflated so beware.