The Korean 420 mL thermal tumbler includes a removable tea filter, but that feature does not mean every drink can safely be sealed inside. Read the drink restrictions as well as the attractive capacity figure.
Check the drink before closing the lid
The official precautions list dry ice, carbonated drinks, salty soups, tea and dairy among contents not to put in the sealed tumbler. Its separate tea-bag answer says to keep the lid open during use because expansion can cause overflow.
Do not treat that open-lid note as permission to seal a brewing tea bag inside for transport. If the instructions supplied with your item are unclear, ask Atomy before using it that way.
Fill and assemble carefully
Check that the silicone gasket is correctly seated and close the cap fully. Keep the liquid below the bottom of the stopper; the nominal 420 mL capacity is not an instruction to fill a hot drink to the rim.
Open the tumbler upright, especially with hot contents. The page also calls for the lower lid section to be firmly tightened so that it does not loosen unexpectedly when opening the upper section.
A loose or incorrectly seated part is a reason to stop and correct assembly, not to test the seal by putting a hot tumbler in a bag.
Clean without heat shortcuts
Use a soft sponge, neutral detergent and lukewarm water, then rinse the drinking parts and interior. Check the gasket before reassembly.
The listed restrictions include no microwave, no dishwasher and no boiling the cap. This guide does not invent a disassembly method for parts whose removal is not described in the supplied instructions.
Source note
Atomy Korea thermal tumbler 420 mL, including its precautions and tea-bag FAQ, checked on 7 September 2026.