So what is this mylar? Some here call it (tracing) paper, others foil.
I assume it is foil, but I’m a bit confused, because for example Tim Roth writes in his 180-project, that he uses tracingpaper (mylar).

Why is it better than “ordinary” tracingpaper?
And when it is really better, which thickness would you recommend??

Grit.

I used google and…

Mylar® is an extraordinarily strong polyester film that grew out of the development of Dacron® in the early 1950s. During the 1960s cellophane gave way steadily to Mylar® with its superior strength, heat resistance, and excellent insulating properties. The unique qualities of Mylar® made new consumer markets in magnetic audio and video tape, capacitor dielectrics, packaging and batteries possible. By the 1970s, Mylar® had become DuPont’s best-selling film, despite mounting competition. Mylar® is now a product of a joint venture, DuPont Teijin Films

and ebay

http://cgi.ebay.ca/MYLAR-2mil-Extrawide-4-1-2-feet-x-100-Pristine-Roll_W0QQitemZ290186396655QQihZ019QQcategoryZ42225QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

i hope it help