Safety
Zojirushi Issues Warning on Proper Use of Thermal Flasks
Japanese manufacturer Zojirushi has advised against storing certain beverages in thermal flasks to prevent internal damage and rust.
On August 5, 2026, the renowned Japanese thermal flask manufacturer Zojirushi issued guidance regarding the proper maintenance and usage of their products. According to the company, while their flasks are designed for water, tea, and coffee, users should avoid storing milk, fruit juices, carbonated drinks, or high-salt liquids like miso soup for extended periods. The company warns that these substances can cause internal corrosion, rust, and a reduction in thermal insulation performance.
For residents and travelers who rely on these flasks, proper cleaning is essential to extend product life. Zojirushi advises against using steel wool or abrasive sponges, as these can scratch the internal coating, leading to the accumulation of odors and stains. Furthermore, unless explicitly stated, flasks should not be placed in a dishwasher, as high heat and water pressure may damage the exterior finish or deform the container.
To maintain hygiene, the company recommends four steps: rinsing the flask immediately after use, disassembling the lid and rubber seals for separate cleaning, and using mild dish soap with a soft sponge or bottle brush. While these guidelines are specific to Zojirushi products, they serve as a general reminder for maintaining thermal drinkware. It remains to be confirmed if these maintenance protocols apply universally to all brands of vacuum-insulated containers.