Thermos: Metal vs Glass - What is the Difference?

  • Thread starter JohnFDS
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In summary, the metal type vacuum flask is cheaper to make and likely less desirable quality-wise. The glass type flask can be fragil, but will last longer with a good insulation vacuum.
  • #1
You all know about this invention (vacuum flask) is someone don't its metal bottle with cup inside is vessel of glass which double walls and vacuum between them, outside of walls is painted with mirroring dye, and there's some sprout on the bottom of vessel (i don't know why).

My question is I've seen them made of pure metal and i want to know can they hold heat as good as ones made of glass? And what this painting and sprout on the bottom are doing?
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  • #2
the walls are mirrored so that no heat radiates out (from the hot contents inside) or no heat radiates in (into the cold contents). i think that the spout you are referring to is the place where from the air inside was sucked out (to create the vacuum). after the air has been sucked out, the glass has to be sealed right, that what results in that spout.
  • #3
With regards to your question of glass versus metal, you would be right to assume that the glass type is superior, since glass(or some variant) does not conduct heat nearly as well as a metal.
But why are there metal thermo's when glass is better? Money.
It's cheaper to make and they hope consumers don't care about quality.
  • #4
Stainless steel is still a pretty good material to make thermos bottles from. Nowadays even lab equipment for low temperature experiments is made from stainless steel. Glass used to be a popular material (there are still plenty of glass cryostats around, I have used a few) but there are a couple of problems.
One is of course that glass is quite fragil, but another problem is that the vacuum in glass containers tend to go soft (=bad vacuum) after a while. The vacuum in a properly stainless steel container will be ok for several years whereas the pressure in most glass flasks tend go up much quicker and a good insulation vacuum is MUCH more important than any conduction losses (which are pretty small assuming the inner container only touches the outer at the neck).

1. What are the main differences between a metal and glass thermos?

The main difference between a metal and glass thermos is the material used for the inner lining. Metal thermos have a stainless steel or aluminum inner lining while glass thermos have a glass inner lining. This affects the insulation properties and durability of the thermos.

2. Which type of thermos is better for keeping drinks hot or cold?

Metal thermos tend to be better at keeping drinks hot or cold for longer periods of time compared to glass thermos. This is because metal is a better insulator and can retain temperature better than glass.

3. Are there any health concerns with using a metal or glass thermos?

Both metal and glass thermos are generally considered safe to use. However, some people may have concerns about the potential leaching of chemicals from the materials into their drinks. In this case, it is recommended to choose a thermos with a food-grade lining and to avoid using it for hot liquids.

4. Can I put my metal or glass thermos in the dishwasher?

It is not recommended to put a metal or glass thermos in the dishwasher. The high heat and harsh detergents can damage the thermos and affect its insulation properties. It is best to hand wash the thermos with warm water and mild soap.

5. How do I choose between a metal and glass thermos?

The choice between a metal and glass thermos ultimately depends on personal preference and intended use. Metal thermos are more durable and better at retaining temperature, making them a good choice for outdoor activities. Glass thermos are more lightweight and may be preferred for everyday use, but they are more fragile and may not keep drinks as hot or cold for long periods of time. It is important to also consider the quality and insulation properties of the specific thermos before making a decision.

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