Fill the balloon with water . This image illustrates why you don't completely fill the balloon you should always leave some room in the neck of the balloon, then as the form dries the pressure has somewhere to go and your clay wont split.
No helium needed to fill balloons. just vinegar and baking soda!No helium needed to fill balloons for parties.just vinegar and baking soda! I NEED TO REMEMBER THIS! this is important since helium is not a renewable source and is in such short supply