Main ingredients of heatproof glass
Silica sandSilica sand
Boric acidBoric acid
Recycled glass
Glass that was not turned into a product is gathered and crushed into uniform pieces that are easily meltable in a furnace and recycled.
All are mixed and melted in a furnace.
The energy used for HARIO's glass melting furnace is electricity. By powering the electrodes, the ingredients and cullet are melted so no exhaust gases are emitted. For that reason, a clean, chimney-free factory was built. HARIO is not only a company that is particular about their reliable and safe materials, but also one that is earth-friendly and considers the environment.
1. Strong resistance to temperature change (little expansion from heat)
2. Excellent durability against chemicals (resistant to acid and alkaline)
Heatproof glass has little heat expansion. Heat will cause glass to expand and contract. However, heatproof glass, compared to normal glass, has less expansion from heat. When pouring hot water in, as shown in the figure, the inside area in contact with hot water will expand, but the outside part that has no contact with hot water will not expand. This is the reason why breakage occurs.
Heatproof glass expands less in heat, so the phenomenon in the figure will most likely not occur and is said to have a strong resistance to heat.
1. Microwave-safe
It is resistant to sudden temperature change and allows passage of electromagnetic radiation.

* Products with metal parts are for hot water use.

2. Prevents the transfer of odor and color
The flavor of coffee and tea will not be lost. It is also good for use as storage containers.

3. Dishwasher-safe

* Hand-painted products are exceptions. For details please refer to the instruction manual.
HARIO's products have a "heatproof certification sticker" (see figure at right) proving that the product is certified by the Glass Manufacturers' Association of Japan (GMAJ) as a heatproof glass product.
Heatproof glass, depending on its use, is separated into different categories. For safe usage, HARIO categorizes the different uses with the signs below and marks them on the products, instruction manuals and package boxes.

When using, make sure you check the signs below.

* The sign on the glass itself is representative of the product's main use. In the case for the "CHJMN (a teapot with glass lid),” you can remove the tea strainer and use in the microwave;
however, since the main use is as a teapot it is shown as "hot water use.”
1. Transparent
2. Prevents odor transfer and dirt *1
3. Will not allow passage of air, gas and liquid *1
4. Hygienic
5. Can present both cheap and expensive products
6. 100% natural minerals *2

*1 Since the glass is hardened after being melted once, the surface is smooth. There is no room for dirt or odor to pass through, nor will air or liquid be allowed.
*2 The raw ingredients are 100% refined natural minerals, making the final glass product 100% all natural as well.
There are 4 different types of glass that we are familiar with. "heatproof glass" , "soda glass" , "crystal glass" and "toughened glass" Their special characteristics are listed below.

Type Heatproof glass
Special characteristic Resistant to sudden temperature change (little expansion from heat).
Excellent durability against chemicals.
Its durability against shock is the same level as soda-lime glass.
Raw Materials Silica sand, borax, boric acid, aluminum oxide
Type Soda-lime glass
Special Characteristic Most normal type of glass.
Vulnerable to heat.
Raw materials Silica sand, soda-lime, ash
Type Toughened glass
Special characteristic Strong resistance to thermal shock
The glass surface will strengthen if it is chemically toughened or if the hot soda-lime glass, still in the process of being generated, is rapidly cooled.
Raw materials Silica sand, soda-lime, ash (same as soda-lime glass)
Type Crystal glass
Special characteristic Highly transparent.
Has a shiny appearance.
Creates a pure tone.
Soft and easily scratched.
Raw Materials Silica sand, lead oxide, potassium carbonate

Heatproof glass has strong resistance to heat. Toughened glass has strong resistance to shock.