Is completely sealed when not just with hot drinks, an overpressure is built up.
And the temperature is kept great. Schicker handle to fold and a strap for clicking.
TEST!
Cold: In 24 hours from 6.3 to 12 degrees = 5.7 +
Warm: From cooking in 24 hours on 61 degrees, in 48 hours to 44 degrees.
Those are very good values in my opinion.
Would I buy again and again!