HARIO’s heatproof glass is manufactured in an ISO9001/ISO14001 approved factory, the Koga Factory.
It is the only heat-proof glass factory in Japan.


Silica sand, borax, and boric acid are delivered into the mixer with the force of air and then mixed. The mixed ingredients are then sent to the all-electric melting furnace via a computer-controlled conveyor.


The center of the all-electric melting furnace is about 1600℃. The ingredients for the heatproof glass only melts at extremely high temperatures. The glass itself can act as a conductor inside the furnace and about 20 tons of glass can be melted per day.

Mold blowing

The 16-head automatic blow-molding machine presses and flattens glass spheres that are heated to around 1300℃. Blowing air into the glass, spinning it, and putting it into a mold, the machine produces an average of 25 products per minute.


The lehr (annealing furnace) heats the glass up to 620℃ and then slowly cools it, which removes the stresses developed within the glass. Removing these stresses makes the next processing step easier.

Machine work

Once in the finishing steps, the product is processed based on the different categories using a computer-controlled chill cut machine that adjusts the size and shape of the glass.


Products with complex and special parts, such as the neck of a syphon bowl or a glass handle, are processed by hand.


Products that have been processed have designs and marks printed on them using a color auto-printer.


The prints are then baked onto the products with a baking furnace called a decorating lehr. The products are then dried.


For completion, the handles, lids, and other accessories are installed, sorted into different categories, and packed into boxes.