That link didn’t work for me, but this one did: http://www.tyvekenvelopes.com/vers_recycle.html. The address appears to have changed since I first looked into it, but still very straightforward. BTW, I got a miserable response when I asked our mailroom about it and decided we really didn’t get enough tyvek to agitate about it. I bug them about enough stuff….
I return the Tyvex envelopes to the sender and ask them both to recycle them through the Tyvex recycling program (link: http://www.tyvekenvelopes.com/rec_how.htm) and ask them to either send me postage in the future for me to use to return them or not to send them anymore.