DuPont in conjunction with Waste Management have developed a nationwide recycling program.
Tyvek® (like extra race numbers that can't be used) can be recycled very easily by putting it all in a box and mailing it to:
DuPont Co.
Attn: Shirley Wright
8401 Forth Darling Rd
Richmond VA 23237
The only restriction is that you can ONLY send Tyvek.
That means NO staples, NO safety pins, NO paper-clips, NO Dag Tags, NO D-Chips, NO paper labels, etc.
As I find and learn more about this I will post all I know here.