Actually, they ARE supposed to be conductive- at least to the tune of about
a megohm. In any operation that is serious about antistatic procedures, the
mats, wrist straps, and other equipment are to be tested periodically. Most
testers show if a mat reads open right away.
If you have mats or other equipment that read open, then you have found
defective hardware. Trash it.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip