A cover from the official periodical of the United States Chamber of Commerce in Germany

This cover was in the lot that I recently acquired. There is a French stamp attached addressed from, Commerce in Germany Official Periodical of the United States Chamber of Commerce in Germany Washington DC and 21 taunus anlage Frankfurt / Main. It's addressed to Mr. P. Piggott, Pres. Pacific Car & Foundry Company which owns Peterbilt, Kenworth, and several other motor companies. It looks like maybe it's some type of commemorative stamp, not really sure but it's interesting. It's made out of what looks like a small brown paper sack. Have any of you guys seen something like this before?

The blue green rubber stamped "IMPRIMES" tells you that the envelope contains/contained printed matter, i.e. business mail.

I am guessing that the Chamber of Commerce in Frankfurt A.M. sent a large number of these, probably mostly to the U.S.A., and in order to save money, mailed them from France at a lower "printed matter" rate.