How long will the balloons stay inflated?

I have two 4 ft. tall aluminum balloons that I am going to fill with air or helium, whichever will last longer. How long will they last before they begin to deflate? I need them to remain inflated for 9 days. Would they stay inflated longer if I were to use helium instead? What is the approximate duration period of the balloons for both regular air from a hand pump and helium, and is there anything I can do to make them stay longer? Thanks!