all the descriptions call it pet.
First, t-glase is made from the highest optical quality PETT material
It's a defintely not pet-g but a co-polymet of pet. Basically pet gets cooked to add the hydrophilic ability and increase the strength, the crystallisation which also makes it less opaque and more transparent:
Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size less than 500 nm) or opaque and white (particle size up to a few micrometers) depending on its crystal structure and particle size.