Heat oven to 200Â°.
Divide popped corn between 2 ungreased baking pans, 13x9x2 inches.
Heat sugar, butter, corn syrup and salt, stirring occasionally, until bubbly around edges.
Continue cooking over medium heat 5 minutes.
Remove from heat; stir in soda until foamy.
Pour on popped corn; stir until corn is coated.
Bake 1 hour, stirring every 15 minutes.