This one is a teaser, because the Clairefontaine Prioritaire airmail envelopes are no longer being imported in the US! These are the larger size envelopes, made to fit A4 size paper. They're pretty straightforward, really. I mean after all they're just envelopes! They're smooth, 90g Clairefontaine paper, very similar to Clairefontaine Triomphe envelopes. In the video I compare the Prioritaire, Triomphe, and G. Lalo Vergé de France envelopes.
The Vergé de France are quite different from the other two. The Vergé de France is a highly textured, hand-laid-style paper (1oog), with a lining on the inside of the envelopes. The Prioritaire and Triomphe don't have that G. Lalo lining, but they are still extremely fine envelopes.
Doing a writing test with the 3 different envelopes (using J. Herbin Cacao du Bresil), all of them perform very well. No feathering, no spreading, and bleedthrough, though quite irrelevant for envelopes, was non-existent. All-in-all, the Prioritaire envelopes are very novel and reminiscent of a time by-gone, but in their absence, the Triomphe and Vergé de France make mighty fine substitutes.
***Update as of 3/23/10*** I was able to get my hands on the last remaining Prioritaire airmail envelopes in the US, available on my website. They are the smaller size ones, not the full size ones like you see in the video.
Link to YouTube for iPhones and full-screen.