Actually, are you refering to the duck that is served chopped up with
skin attached to the meat, (which is the Cantonese version), or the
skin served as a separate course? The "blow up the skin like a ballon"
trick is usually used for Peking duck. It separates the skin from the
meat, making it extra crispy during roasting, so it can be removed from
the cooked duck and served wrapped with a flour pancake.