At what temperature does a polyester release toxic gases?

I've bought a "Shrinky Dinks" printable sheets and now I'm feeling unsure about using it since I've read that heating polyester materials may be very harmful for health, and the final purpose of this material is to melt it at about 325°F.


Searching on the web I've noticed that the information isn't that straightforward about the product. Even on the official website, where they do mention about having specific certifications, I cannot understand them fully since I'm not used to all the technical language they use.


That's why my question is about the temperature I can safely heat this material at.


