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Principle of a Thermos Flask and Rang Dong’s Product Updates

October 2nd, 2023

Many people have been using thermos flask as the device conveniently keeps hot and cold drinks/soups for many hours. It becomes quite handy when we need to go out for shopping, going to work or school, or camping. The thermos flask’s heat retention is in place thanks to its special structure.

History of thermos flask

In 1892, a vacuum flask was invented by a Scottish scientist, Sir James Dewar. He made a partial vacuum to keep the temperature stable. Six years later, he hired a glassblower to make a sturdier flask and it became commercial with the name of “Dewar Flask”. The glassblower, Reinhold Berger, and his partner Albert Aschenbrenner gave the metal body casing and secured a patent for the flask. In 1904, the pair renamed it ‘Thermos’, using the Greek word for ‘hot’.

Inside a thermos flask

The thermos flask has a body and inner parts. The body is made from plastic or stainless steel. Inside the thermos, there is a glass linear refill and a silicon neck’s stopper above. Another stopper in the bottom keeps the glass refill in place and vacuum. The glass refill is silver coated that looks like a mirror.


Rang Dong’s safety glass refill has high heat retention in compliance with European and Japanese standards.

Heat transfer and thermos flasks principle

Heat transfers in three ways: conduction, convection and radiation. Conduction means heat is transferred by collisions of atoms. It means an atom moves to another. They stop moving when the temperature is absolute zero. Convection is a property of liquids and gases. When liquid or gas gets hot, convection rises above the rest of the body of liquid or gas. That's why we blow the hot liquid to cool it down. Radiation happens when the atom is unstable. They gain extra heat energy and make the atoms quickly return to their normal state. 

The glass refill has silver coating that will reduce heat transfer by radiation. The tight stopper prevents air from entering or leaving the flask. It reduces convection so heat can’t escape from a thermos flask and the drinks stored inside will stay at a stable temperature for several hours. 

When we open the stopper, the heat escapes a bit but our beverage’s temperature will not change much. The vacuum between two walls of the glass refill prevents heat from going through convection and the thinness of the glass refill prevents the heat from entering or leaving through conduction. The body adds more insulation. 

Rang Dong’s thermos flask is simple, effective and convenient

The heat cannot go through a vacuum, so it keeps our beverages hot or cold at steady temperatures.

For 60 years of establishment and development, Rang Dong has emerged as Vietnam's leading manufacturer of thermos flasks, accounting for more than 90 percent of the market share.

Rang Dong offers various types of thermos flasks, a reliable assistant to our drinks.

The good-quality body is reducing the three processes of heat transfers. Rang Dong’s thermos flask comes from modern automatic production lines with high efficiency electric furnace and state-of-the-art glass melting technology. The system emits no CO2, SO2 or dust into the environment. The glass refill meets European and Japanese standards. The body has a stylish, luxuries design and is produced by premium PP plastic, silicone and TPE gaskets. It is certified by Swiss company SGS for health safety and durability, anti-rust and durable ornamental steel and high-grade stainless steel. 

Rang Dong applies quality control systems such as ISO 9001: 2015, ISO 5001:2011, ISO 14001:2015, 5S, Kaizen, LEAN, 6 Sigma and BSCI. All products are tested in accordance with the British standards BS EN 12546-1: 2000. 

Rang Dong’s products have won trust by consumers both at home and abroad. The Hanoi-based company has so far exported over 25 million units of vacuum flasks and glass refills all over the world, with destinations in more than 22 countries including Japan, Singapore, China as well as many European and South American countries.  

For more information, please watch the video of Rang Dong's thermos flask production line.

Should you have any questions, wish to share your ideas about vacuum flasks or request a quotation, please send us an email to: export@rangdong.com.vn.

Our website: vacuumflask.rangdong.com.vn

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