You'll be hard pressed to find true PET (Polyethylene terephthalate) filament, as most PET filaments are actually copolymers - PET with an extra molecule. The most common, PETG filament, is an industrial strength filament with several great features. Figuratively speaking, it combines the ease of use of PLA filament with the strength and durability of ABS filament. First, its strength is much higher than PLA and it is FDA approved for food containers and tools used for food consumption. Unlike ABS filament, it barely warps, and produces no odors or fumes when printed. PET filament is not biodegradable, but it is 100% reclaimable. It's known for its clarity and is also very good at bridging. PET 3D printing filament is available in 1.75mm and 3mm. For tips and tricks on 3D printing PETG, check out How To Succeed When Printing With PETG.