Preheat oven to 225 degrees F (110 degrees C). Grease a large baking sheet. Place popped popcorn in a large bowl.
Combine sugar, corn syrup, and butter in a saucepan; bring to a boil until sugar dissolves, about 3 minutes.
Combine drink mix and baking soda in a large bowl; pour sugar mixture into drink mixture, stirring carefully. Sugar mixture will bubble. Pour mixture over popcorn; toss to evenly coat. Transfer coated popcorn to baking sheet.
Bake in the preheated oven, stirring every 10 minutes, until coating has hardened, about 30 minutes. Cool and break popcorn into pieces.
