@galannthegreatWhen you're doing toner transfer you'll need to apply enough heat to melt the toner (the toner has a plastic component in it). When using an cloths iron you're supposed to set it to it's MAXIMUM temperature, with the steam OFF. Using the cloths iron is usually how this transfer is done: there are other solutions, like using speciality presses (the Press-n-Peal guys sell such a press) or passing the PCB+Film throw a modified laminating machine.
@frodoit is fine to use a clothes iron with that but don't apply to much heat because too much heat makes the plastic sheet melt.
That film is designed to be used in a Laser printer. The laser printer has a oven inside that heats whatever passes throw it to a maximum of 200 C (according to some sources, it's difficult to find such details). I doubt they used an plastic that melts easily, they had to use a plastic that survives the laser printer. You can see proof of the existence of the oven in laser printing devices: have you noticed how paper out of laser printer is worm? Same is true for Xerox-type machines.
