Your thermos is leaking because of the gasket

If your thermos is leaking in your lunch bag, the gasket is probably dirty, worn, or just not seated right.

Take the lid apart and wash the little rubber ring. Food gunk breaks the seal. Dry it, snap it back into place, and that fixes most leaks.

Second, don’t fill it all the way to the top. Leave a little air space. When you screw on the lid, the air compresses and pushes liquid past the seal. Half an inch of room prevents that.

Third, test it: fill with water, close it, and turn it upside down over the sink. If it leaks, the lid is the problem. If not, you’re probably carrying it sideways or the pressure from hot liquid is doing it. And if your lid has a button or vent, make sure it’s locked shut.

Your lunch bag will thank you.