My Primus Vacuum thermos/mug/lunch jug is very difficult to open. Why does this happen and what can I do to prevent it?Updated 21 days ago

With our vacuum sealed drinkware, this issue might occur sometimes. When the thermos is opened and air is let in, in combination with the liquid cooling down over time, underpressure develops. This makes it so that the lid is being sucked in, so that the vacuum is mantained, which can make it very difficult to open the thermos.

Despite this, there are still some measures you can take to prevent this problem from occurring as often.

Please try to fill up your vacuum thermos as much as you can, this prevents extra air from filling up your thermos and creating underpressure.

Furthermore, it helps to open the thermos fairly regularly, just for a short moment, to make the underpressure disappear.