"The commercial applicability of polyethylene is limited by its low melting point compared to other thermoplastics…The melting point for average, commercial, lo

"The commercial applicability of polyethylene is limited by its low melting point compared to other thermoplastics…The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F)." -- so you could carefully get your tea steaming hot without melting polyethylene, but it doesn't sound like something I'd prefer to do. Metal vessels really have a lot going for them when it comes to heating foods over flames or coals!