For the most part, "generic" (e.g. Costco
"brand") fax paper works just fine
in both of my 700s. However, the "real" paper that came with one of the
units (I have one almost unused roll left) prints a much darker tone in
both machines, suggesting it is more sensitive to heat than "garden variety"
(presuming Costco sells garden variety) fax paper. I have yet to try more
than one other brand (a roll of "panasonic" paper - lord knows who really
made it) and it also prints "light."
I am starting to feel really guilty about the Silent 700 I left in the
Goodwill AS-IS (next stop the dumpster) area, but in any case it had a roll
of light green paper in it. This was the earliest unit I think I have seen
too, a huge suitcase as opposed to briefcase sized unit, dated I think
about 1973.