Pop corn according to package directions.  Sort through popped corn and toss any kernels that did not pop. Place popcorn in a large over sized bowl or pot that will hold all of the popcorn.  Preheat oven to 250 degrees. In a medium saucepan, combine sugar, butter and corn syrup.  Bring to a boil over medium heat.  Once it is boiling, boil for 4 minutes stirring constantly.  Remove from heat and stir in baking soda and vanilla. Pour hot mixture over popped corn and stir well to combine.  Divide mixture in half and put each half on a cookie sheet.  Bake for 30 minutes, stirring each tray after every 10 minutes.  Cool.  Store in airtight container.