Tyvek is a durable, long-lasting material so is great for using in your wallet. If you have a black
wallet, use the brown envelopes.
Why long lasting? Because if you make the standard Tyvek
envelope into a Himber type, you want to keep them as long as you can without remaking them all the
time.
By the way, I basically make the Himber Tyvek using Richard Osterlind's double envelope
technique. Easy to make and they are better than the pre-made Tyvek Himber.