Even though Tyvek, in this size envelope, is not a common sight for the average person, they will last.
PLEASE NOTE: These are the envelopes, NOT the Himber envelopes!
HOWEVER - if you have the Osterland method of making a double envelope, you can make a Himber envelope out of two of these envelopes using a strong glue stick and basic arts and crafts.
You can even make an envelope with a flap on each side that will look like the Tyvek Himber you buy but, I think, even better than the bought one.
The Osterland book is "Diverse Deceptions".

These are normal envelopes (I already complained about the Himber ones on its respective review).

Pros:
- Tyvek paper: lasts forever (almost)
- Fits a playing card: awesome, because regular #3 envelopes that I buy online don't fit a poker size card

The only con:
- The slits are horrible. Vertical envelopes should have no slit, or if they do at least don't make them straight... They should have been a shorter half-moon slit as in the other envelopes from Alan Wong. It's not smooth to close and when you open it to show it empty it looks really weird because the slit makes the envelope buckle differently.

I'm personally not happy with the design, but they still can be used in performance