Five key facts about glass refill in a vacuum flask

Many thermos users may wonder about the structure and principle of the glass refill for vacuum flask, what is the best type or if the black dots visible on the surface of a glass refill are going to affect our drinks. Let's check the following facts of a glass refill to see if these factors have any impact on the quality of the vacuum flask or the beverage kept inside.

Glass refill structure

A thermos bottle minimizes energy transfer due to convection, conduction

The glass refill is made from neutral glass, which is popularly used in the medical field to make syringes as it is safe for users' health. The component consists of two glass 'jars' being put as one in another, separated by a layer of vacuum. The outer layer of the inner flask and the inner layer of the outer flask are coated with silver, thus it is not in direct contact with the liquid kept inside the refill.

Glass refill colors

The glass colors make the colors of the glass refill. The three main colors are white, light green, and light pink. Manufacturers use different glass refill colors to refine the quality of the component.

White: glass refill of this color has a higher silicate and borax amount than similar products, which gives the glass strong reliability, permitting it to withstand high temperatures, impact, and pressure.

Light Pink: indicates good-quality glass.

Light Green: the color indicates a high content of iron dioxide, so the glass has poor quality

Black spots in glass refill

Glass refills with spacers (right) and without spacers (left).

Normally, between the two jars, manufacturers would place three pads to fix the position of the glass refill. Looking from outside, we can see three black spots around the bottom. They do not come in direct contact with the beverage kept inside so they won't cause any harm to human health.

Heat retaining feature

The glass refill structure helps conduct less heat than other materials such as iron or stainless steel. The vacuum between the two walls prevents heat movement through convection and the thinness of the glass refill prevents heat from transferring inside out.

The silver-coated Nitrate between the two jars restrains the heat radiation.

Glass refill reliability

The glass refill can withstand pressure when filled with water and drops from as high as 10 cm to the ground. However, to ensure the life of the glass refill, the thermos should be placed in a safe, balanced place to avoid strong impacts and drops.