How to Clean a Thermos Flask

Why Thermos Flasks Need Regular Deep Cleaning

A thermos flask's narrow opening and vacuum-insulated walls make it harder to clean than a regular bottle. Coffee, tea, and soup residue builds up inside, leading to stains, odors, and eventually bacteria growth. Regular cleaning keeps your thermos hygienic and odor-free.

What You'll Need

• Dawn Platinum Dish Soap
• Bottle brush with long handle
• Cup lid gap cleaning brush set
• Bottle Bright cleaning tablets
• Baking soda
• White vinegar

Daily Cleaning After Every Use

1. Disassemble the lid and any removable parts
2. Rinse the flask immediately with warm water
3. Add a drop of dish soap and hot water, then scrub inside with a long-handled bottle brush
4. Clean the lid with a lid gap brush, paying attention to threads and seals
5. Rinse all parts thoroughly and air dry with the lid off

Deep Cleaning: Bottle Bright Method

1. Fill the thermos with warm water
2. Drop in one Bottle Bright cleaning tablet
3. Let fizz and soak for 15–30 minutes
4. Shake gently, then rinse thoroughly
5. Soak the lid parts in a separate bowl with another tablet

Bottle Bright is safe for stainless steel and removes stains and odors without harsh chemicals.

Deep Cleaning: Baking Soda and Vinegar Method

1. Add 2 tablespoons of baking soda to the thermos
2. Pour in ½ cup of white vinegar — it will fizz
3. Fill the rest with warm water
4. Let soak for 30 minutes
5. Scrub with a bottle brush, rinse thoroughly, and air dry

What to Avoid

• Dishwasher: High heat damages vacuum insulation and can warp lids
• Bleach: Can damage stainless steel and leave harmful residue
• Abrasive scrubbers: Scratch the interior and exterior surfaces
• Soaking for too long: Extended soaking can affect seals and gaskets

Final Thoughts

A long bottle brush for daily cleaning and a weekly Bottle Bright soak are all you need to keep your thermos flask clean, stain-free, and odor-free. Always store with the lid off.