Quick answer

Most Mepal thermos flask leaks are caused by a misaligned or worn silicone gasket, a loose cap, or debris caught in the threads. Start by checking the seal and tightening the lid. If the leak persists, inspect the gasket for cracks or flattening and replace it if necessary.

Common Causes of Leaks

The most frequent culprit is a dirty or misaligned silicone ring inside the cap. Food particles or mineral deposits can prevent a tight seal. Another common cause is overfilling: if you fill the flask past the recommended level, pressure changes can force liquid out through the vent. Finally, a cracked or deformed lid – often from dropping or exposure to high heat – can create a permanent leak path.

Step-by-Step Fixes

First, disassemble the cap completely. Remove the silicone gasket and wash both the cap and gasket in warm, soapy water. Rinse thoroughly and dry. Reinsert the gasket, ensuring it sits flat in its groove. Next, fill the flask with cold water, close the lid, and shake gently while holding it over a sink. If no leak appears, the problem was debris. If it still leaks, inspect the gasket for flat spots, cuts, or brittleness. A damaged gasket needs replacement – check Mepal's spare parts or contact support. If the gasket looks fine, the cap or flask body may have a hairline crack; in that case, replacement is the only reliable fix.

Preventive Care Tips

To avoid future leaks, always rinse the flask and cap after each use, especially if you store sugary or milky drinks. Hand-wash the gasket periodically and avoid putting it in the dishwasher if the manufacturer recommends against it – high heat can degrade silicone over time. When closing the lid, align the threads properly and tighten until snug, but don't overtighten, which can warp the seal. Store the flask with the lid slightly loose to allow airflow and prevent odor buildup.

Leak Diagnosis at a Glance

  • Symptom: Water seeps from around the cap when the flask is tilted or shaken. Likely cause: gasket issue or loose lid.
  • Likely Cause: Dirty or misaligned silicone gasket, overfilling, or damaged cap threads. Check and clean the gasket first; overfilling is also common.
  • Corrective Action: Disassemble, clean, and reassemble the cap. If leak persists, inspect gasket for damage and replace if needed. If gasket is intact but leak continues, the cap or flask may be cracked – replace the part.

Products That Help

  • Insulated sports bottle Twist 600 ml - Ceramic white: The Twist sports bottle keeps drinks at temperature for up to 6 hours. With straw, carrying loop and dishwasher-safe, ideal for on the go. Its dishwasher-safe design makes cleaning the seal and cap easy, reducing the chance of debris-caused leaks. The carrying loop also helps prevent accidental drops that could damage the lid.