X-Zone by Masuda

The magician takes out a deck of cards that look quite strange. A red deck of cards inside a red card case is crossed by a blue deck of cards. He pulls out the blue deck and proves it to be a full deck. Then the performer pulls out the red deck from the case, which also turns out to be a full deck of cards.

NOTE: This is meant to be more of a puzzle than a trick. So what's the puzzle? Think about it. If you stack and intertwine two decks of cards together, the thickness of the stack would be too high to fit inside a single card box. How on earth can an entire deck of blue cards be added to a deck of red cards and still fit within a card box?