Can a thermos go in the dishwasher?

Short answer: usually not. Check your flask's instructions, but most vacuum-insulated bottles are labelled hand-wash only. Here's why.

What the dishwasher does

• Heat can stress the seal that holds the vacuum between the two walls. Lose the vacuum and your drink goes lukewarm.
• Strong detergent can dull or peel the outer powder coating and printed designs.
• Spray arms barely reach inside a narrow neck, so the bottom often stays stained anyway.

What about the lid?

Some lids are top-rack safe, many aren't. Even when they are, the seal groove rarely gets fully clean in a dishwasher.

The easier way

A fizzing tablet does the work by itself, reaches the lid and straw and is gentle on your flask. You just wait and rinse.

1. Warm water in.
2. Drop a tablet and let it fizz with the lid off.
3. Soak the lid and straw in a cup of the solution.
4. After 15–30 minutes, rinse well.

Bottom line

Keep your flask out of the dishwasher unless the maker clearly says it's safe. A weekly fizz keeps it clean without the risk.