The glass is borosilicate, most commonly known as Pyrex. (Pyrex is a brand name) This is the same glass that your kitchen cookware is made out of, and laboratories use for general glassware. The reason that we chose Pyrex is because of it’s good thermal properties and durability. Pyrex is known for it’s impact resistance and also thermal shock resistance. The working temperature of the cup is 914F (490C) maximum. The reason that we don’t recommend walking the cup is because of the higher temperature when the glass contacts the metal next to the weld pool it will cause premature stress (hot spot) on the glass, and will cause premature failure. As long as the cup isn’t resting on the metal and there’s no contact with the weld there’s no concern for premature breakage. The other consideration is, there is always gas flowing past the cup which keeps the cup cool.
Stress is introduced into the glass starting at 950F (510C).
The O-rings are high temperature silicone that’s rated to 400F (204C). They are very chemical resistant and we haven’t had one replaced because of melting.