It is a soba cup that is not heat-resistant glass; is it okay to put it in the dishwasher?

Although you can use a dishwasher, the cup itself is not made of heat-resistant glass designed to withstand heat^[1][2]. The soda glass used in the soba cup is a material commonly used for everyday tableware; while it withstands gradual temperature changes, it tends to be vulnerable to sudden temperature fluctuations^[3]. This is why care is needed before and after the washing process, even if it can handle the hot water inside the dishwasher itself^[4].

In particular, if wrapped with a wet cloth or placed in a low-temperature area while the cup is heated hot, there is a risk that the glass may break due to rapid cooling where the temperature drops in an instant^[5]. A similar thermal shock can also be inflicted if it comes into direct contact with cold air immediately after finishing washing, or when rinsed with cold water.

While you can enjoy the convenience of a dishwasher, hand washing is recommended to preserve the vessel without flaws for a long time^[6]. Simply wiping it gently with a soft sponge and lukewarm water allows you to avoid breakage from thermal shock and care for the cup safely.