here a better answer from one of our engineers (we do nothing else than research and development of plastic container)
The softening point of PET is above 75°C, or 167°F. It’s a bit of a range, though, so you want to keep well below that temperature. There’s no real basis that I know of to claim that PET harbors bacteria any more than glass does, and PET has to pass the same regulations for food contact that other materials have to pass.
Plastics are permeable to gases and water. PET is a good barrier to water, CO2 and oxygen, but some does permeate in over time. HDPE is an excellent water barrier, but a very bad oxygen barrier. I wouldn’t expect honey to be oxygen sensitive, though. I definitely wouldn’t do mead in plastic because of the oxygen permeation problems. In that case, you need to worry about the closure too, since if it’s polypropylene, it’s going to be a bad barrier as well.