The PET grades used for 'ovenable' trays have the same basic chemical formula as ordinary PET but it has been specially heat treated during the container manufacturing process to turn it opaque milky white. In this form it has a much higher temperature resistance and is can be heated up to 220 degrees centigrade which is high enough for reheating pre-cooked foods.

Again, this depends on the shelf life requirements. Many brewers package beers in short life applications for uses such as at football games where there is a need to remove glass for very obvious safety reasons.  PET grades used for soft drinks do not quite have the longer life resistance to oxygen ingress to protect against deterioration in taste that is demanded by the brewers.  New  PET developments in co-injection technology and special monolayer polymers are delivering a highly improved oxygen barrier more suitable for these applications.   With this new advantage, plus its light weight and strength, PET is now being used to package and transport beer.