Adair’s Gozinta Envelopes

An astounding illusion like the Gozinta (or In & Out) Box but performed with Red & Blue Envelopes.
The Magician removes a blue envelope from inside a Red One.
He then places them on top of each other to show both are identical in size. Then to the surprise of everyone he inserts the Red envelope into the Blue one. 
Supplied are two special envelopes along with the instructions and ideas for their use. Envelopes measure 4.2″ x 4.4”
This is a 2D version of the popular 3D prop. The imaginative performer can also use the envelopes to change a card. For example a card pulled out of the red envelope, which was inside the blue, as a prediction, – which proves to be wrong. 
So he now places the blue envelope inside the red to “warp them through space” and when the card is now removed from the inside envelope (blue) it has changed to the correct prediction card.
A novel effect, at a very low price.