The fusing unit of a normal copier can easily reach 180 degrees Celsius. Besides ruining your transparencies, you might also seriously damage the machine you used. Copy shops will merciless force you to pay for that, so the investment in
heat-resistant transparencies is saving you money in the long run. Transparencies nowadays go the way of other outdated
presentation media and are replaced by
data projectors.
A word about the fusing unit :
After the toner has been transferred to the paper/transparency, it has to be melted onto the surface. One very easy way to do this is the use of a heat roller, which works like a very small version of the contraptions used to iron bed sheets. Another principle uses halogene lamps - with the disadvantage of the paper igniting in case of a paper jam. One old, magnetographic printer, the Bull MP6090 used three of those lamps and was equipped with tiny fire doors and a built-in vacuum cleaner.