Tyvek Himber Envelopes are great utility poker card size, double sided himber envelopes, brown color, made in very durable tyvek material.

They are made for switching and multiple outs:

Switch any freely chosen card into your force card
Use any two force cards and reveal either one as your prediction
Use two double face cards in one envelope to have four possible outcomes
Use any blank card with any words, symbols and numbers for the above applications

I use two of them in my magnetic Himber wallet and there are four outs but spectator sees one envelope and one card.

Comes with 2 tyvek envelopes. No instructions included.

Tyvek Himber Envelopes (2 pk.) by Alan Wong