Preheat oven to 200. Pour puffed corn into a greased roasting pan. Combine butter, sugar, and corn syrup in a medium saucepan. Cook on medium heat, stirring constantly until the mixture begins to boil. Lower heat and let simmer for 2 minutes. Remove mixture from heat and add vanilla and baking soda. Stir thoroughly. Carefully pour hot caramel over the puffed corn. Stir making sure all corn is coated well. Place roasting pan in the oven. Bake for 45-60 minutes, stirring corn every 15 minutes. Remove corn from the oven. Pour mixture onto greased waxed paper. Spread out evenly to cool. Once cool place in an airtight container.