Examining the Safety of Putting a Thermos in the Microwave

Can you put a thermos flask in the microwave?

The question of whether or not it is safe to put a thermos flask in the microwave is a topic of much debate. While some people argue that it is safe to use a thermos in the microwave, others strongly advise against it. In this article, we will examine the arguments on both sides and provide alternative options for heating your food or beverages.

Why some people say you can put a thermos in the microwave

  1. Thicker metal walls: One of the main arguments for putting a thermos in the microwave is that the stainless steel used in thermos construction is significantly thicker than other metal objects that can cause sparks or explosions. The thicker walls of a thermos are believed to prevent excessive heating and eliminate the risk of sparks.
  2. Lack of sharp edges: It is generally believed that sharp corners and edges of metal objects are more likely to cause sparks in the microwave. Because a thermos is round and has no sharp edges, proponents argue that it is less likely to produce sparks when used in the microwave.
  3. Open the lid: When heating the contents of a thermos, the lid is typically opened, preventing excessive pressure buildup that could lead to an explosion. Proponents of using a thermos in the microwave argue that the lack of pressure buildup reduces the risk of accidents.

Why you should avoid putting a thermos in the microwave

  1. Uncertainty about wall thickness: It is difficult to determine the exact wall thickness of a thermos. If the walls are thinner than expected, there is a potential risk of overheating and sparking. In addition, some thermos products may be made with reactive metals that could react negatively in the microwave.
  2. Uneven and slow heating: Because of the thick metal walls of a thermos, heating food or beverages inside can be a slow and inefficient process. Heat can only enter from the top, which is a relatively small opening compared to the volume inside. As a result, the food may not heat evenly, and the entire heating process can be time-consuming.
  3. Unreliable terminology: When discussing the safety of using a thermos flask in the microwave, some advocates use phrases such as “highly unlikely” to describe the chances of accidents. This terminology raises concerns about the true level of risk. Metal is known to react in microwaves, and the use of uncertain terms can make claims less credible.

Alternative products to consider

If you prefer to err on the side of caution and avoid putting a thermos in the microwave, here are some alternative products that can keep your food or beverages warm:

  1. THERMOS Microwavable 12-ounce Food Jar: This food jar features a stainless steel outer container for insulation and a microwave-safe Tritan co-polyester inner container. It can keep food hot for up to 4 hours and cold for up to 6 hours.
  2. Mora Double Wall Microwaveable Travel Mug: This travel mug is double-walled and made of ceramic clay, which is excellent at retaining heat. It contains no metal and is microwave safe.
  3. S’well Stainless Steel Triple Insulated Travel Mug: While not microwave safe, this triple insulated stainless steel travel mug is highly effective at keeping beverages hot or cold for extended periods of time. It is a stylish and reliable option for use on the go.
  4. YBOBK HOME Insulated Thermal Bento Box Microwave Safe: This stackable lunch box set features a food-grade stainless steel exterior and a microwave-safe, BPA-free plastic inner container. It allows you to separate different elements of your meal and keep them at different temperatures.

Bottom line

In conclusion, the question of whether or not you can put a thermos flask in the microwave remains controversial. While some argue that a thermos with thicker metal walls, no sharp edges, and an open lid can be used safely, others warn of the potential dangers and inefficiencies. Ultimately, it is up to you to decide if the potential risks are worth it. However, if you prefer to avoid using a thermos in the microwave altogether, there are alternative products that can effectively keep your food or beverages warm.


Can I put a thermos flask in the microwave?

Answer: While there are varying opinions on this topic, it is generally not recommended to put a thermos flask in the microwave due to the risk of sparking, explosion, and uneven heating.

Why do some people say it is safe to put a thermos in the microwave?

Answer: Some arguments in favor of using a thermos in the microwave include the thicker metal walls of the thermos, the lack of sharp edges that can cause sparks, and the fact that the lid is open, which reduces pressure buildup.

What are the potential risks of using a thermos in the microwave?

Answer: Risks include uncertainty of wall thickness, which can lead to overheating and sparking; slow and uneven heating due to thick metal walls; and the use of uncertain terms when describing safety, which raises concerns about the true level of risk.

Are there alternative products I can use to heat my food or drink?

Answer: Yes, there are alternative products designed specifically for microwave use, such as microwaveable food containers and ceramic travel mugs. These products provide safer and more efficient heating options.

How can I be sure my food or drink is safe to microwave?

Answer: The best way to ensure safety is to use containers and products that are labeled as microwave safe. In addition, following the manufacturer’s instructions and guidelines for microwave use is critical to preventing accidents and maintaining food quality.

What are some alternative ways to keep my food warm in the microwave without using a thermos?

Answer: Alternative methods of keeping food warm include using insulated lunch boxes, thermal bags, or electric food warmers. These options provide a safer and more controlled way to keep your food warm without the risks associated with using a thermos in the microwave.