|—Thermos, "Alternate Reality Show"|
Thermos is a hyperactive person who is almost always seen screaming loudly. While he usually screams for no reason, he is occasionally provoked to scream because of his fear of Black Hole. Since he is assumed to be filled with coffee, Thermos's hyperactivity may be a result of the large amounts of caffeine, as he even has difficulty sitting still amongst the other competitors at the elimination. As a competitor on Inanimate Insanity Infinity, Thermos' screen time is limited, as Salt and Pepper dominate the show. He is described as "totally zany" by Pepper.
Thermos is a silvery vacuum flask with two black bands going around the circumference of his body, with one band going around near the top of his body, and one band on the very bottom. He has no cap or lid on, and presumably, coffee can be seen inside. Both when he screams and when he doesn't, his eyes can be craze-looking despite his fear.
Thermos is first seen in "Alternate Reality Show" immediately screaming as Test Tube and Lightbulb travel into the future to the Infinity Timeline using their Time Traveling Calculator. He continues to scream as other Infinity contestants introduce themselves, but he is later hushed by Pepper, who is irritated by his screaming. During "Just Like Me!", Thermos stands as a base for the pyramid of contestants while Lightbulb paints them and later appears jumping on a trampoline with Lightbulb. He makes a final appearance during the elimination, where he excitedly jumps in the air.
- Thermos is the second character to be named after a licensed property. The first is Poptart.
- Thermos' description as "totally zany" by Pepper may be in reference to his voice actor, Niall Burns, who goes by the screenname XanyLeaves.